Okay, I am sure their are many that will weigh in and I hope they do. Since I've got a bit of spare time, I will try and answer the best to my ability what your asking. Please keep in mind, it comes down to personal preference, what you consider a threat, how comfortable you are with a particular apparatus. If you don't believe me..see the 1, 2, and 3 point thread that we have in the firearms forum. Their is no wrong or right, just a personal preference....stealing from my friend Roninsensei. Check his great video and you'll begin to understand my slant on certain preps and yes, sure as you can call me BOB, I am sure someone will have a different opinion. That's why we call this site a forum, mind you I am a bit more cynical than most, maybe too many times hitting my head after a jump, rappel or just walking into doors...lol.
So lets break this down with the mask. First, I know their are those that love those cheap $#% gas masks made in Czechoslovakia like the old M-17 gas mask...wonder why the U.S. crapped out on them, because no one in the military could get those filters changed in the time required to get them changed out in a contaminated environment. While the Air Force was one of the first to start looking for a substitute because aircrews disdained the M-17, they ended up with the MCU-2P. Dont' get me wrong, the NATO circular filter is great and the MCU-2P gives you great vision both peripheral and front vision, but in combat because your opponent can latterly tear it away from your face, is not my first choice for use in combat. Finally the Nattick boys came up with a great replacement for the M-17, modeled off the M-17, but with a circular NATO CBRNE filter. This eventually after some design feedback became the M-95. You can find some good quality MCU-2P's and M-40's from some very reputable mask companies. Personally, I'd stay away when it comes to CBRNE equipment away from those GI surplus stores. When you purchase the mask, use the following documents to inspect them. I've attached them for your use and for others who decide they need the T.O's. Here is the only challenge that we all have...quantitative testing for leaks. Unless you have a test kit (made up of swabs and concentrated oil (smells like oranges), your not going to know if the mask leaks. So my SOP states the filter mask is a mask for use to get out of a contaminated area, I'd make sure I wasn't working in the contaminated zone using these masks.
So now is where I am going to get hit by those that don't believe in the CBRNE issues....I have a PAPR mask for my entire family. I advocate them for my team members, but like I said, its cost prohibitive, but the PAPR offers one thing cartridge masks don't...that is they provide positive air pressure around the entire inside of the mask, preventing contamination from entering the mask. The only issue I'd recommend not using is when your dealing with a virulent virus...in that case the only alternative is what the Self Contained Breathing Apparatus...these are very expensive, unless your a volunteer fireman or an active fireman. Not even Law Enforcement guys have these...typically you will see the CDC folks wearing them in a unknown outbreak until the virus or suspected antigen is confirmed.
As for the rest of the CBRNE gear...you should have a suit (JSLIST are the best, but expensive), if not any charcoal impregnated suit (with a good expiration date), butyl rubber gloves with at least three pairs of cotton inserts, over boots (rubber like the galosh type, make sure you have a size that is one size up to save you from taking them off later), and in the case of the mask, a hood that matches the mask. Also, I'd get some tape...even duck tape will work (used to seal your gloves and boots to the over garment. If you plan to do any sampling of said, virus...then I'd be looking at a level suit or bubble suit.
As for best mask that protects you...can't say, nor recommend one over the other...that is a person's preference...but when you buy your cartridge, make sure they fit the mask and are rated CBRN with at least a 2 to 3 year shelf life. Store them in a cool, dry and dark place, make that a policy for all your CBRNE equipment. Store them in an airtight container and do not store them in the garage near chemicals. Note any exposure to heat, like food will cause the cartridge to lose their shelf life. I store all my CBRNE equipment in the home, in a temperature controlled environment and ask my kids to remove their mask in the summer from their BOB bag and make them carry it back/forth from their rig. Also intense heat cause the rubber on the mask to dry out and make the mask unserviceable.
I use this company and 3M directly for most of my CBRNE stuff.
http://www.approvedgasmasks.com/
Chest Rigs. well that's like you asking which company is has the best armor...like buying a car or pickup. How much money do you have? What style do you like. Remember when the military buys our stuff, we get mostly the lowest bidder..that is how GSA and the rest buy the mil standard stuff. As for what to carry, well you'll need at least a IFAK, magazine pouches that match your magazine/weapon. I wear a detachable map case and a few other Molle items. Since I don't have to worry about gernades as a civilian, they do make an excellent storage item for a compass, a small survival kit, and yes I know, but allows me to attach a water mule to the back of my rig.
So chest rigs. Here are a few videos...Just remember I am not in love with Maine Prepper, but since I don't make videos. LOL love the Hand Model..inside joke between Roninsensei and me. You can google other sites or just look at the manufacture site, they normally have a great marketing videos.
My first body armor was the old style Point Blank stuff, I wore a standard LBE over it. In my deployment to Iraq I wore a MSA Paracleat RAV that my wife bought for me. As I said the military buy from the lower bidder...standard issue. Now I own Cyre Precision gear, a bit more costly, but well again a preferenace issue. I'll give the German's credit for the "Fritz" helmet...the first generation of Kevlar helmets were bulky and well not always operationally suited for the line of work of urban warfare. Since the early 2000's companies have perfected the design to the point...that today, any company with the latest generation of Kevlar helmets...will improve your survivability. I've seen some great ballistic videos on different helmets, so again its wearers preference and well cost. Please remember I am not a salesperson, I just got some good feedback from my friends who bought the Cyre stuff and they made me a believer...also its lots less weight on the noggin compared to the old Fritz Kevlar and I have about 6 or 7 of them in different sizes in by storage unit. You can pretty much pick them up anywhere.
http://www.cryeprecision.com/C-119/Armor-+-Equipment
As for body armor....well definitely don't wash the darn thing, it will degrade the inner soft armor. As for your comment regarding the Level III and Level IV plates worn together. Why would you? I would stick with the Level IV with an early manufacture date and inspect it thoroughly....for me that means buying it directly from the company. Any cracks or anything that looks like out of the ordinary....yeah, some guys will paint over the scratches to make them look new. Me, they are unserviceable, but sure you want to wear two...good luck...just seems like a bunch of weight.
Well I am out of steam for writing today...I am sure their are many that will weigh in...good luck. By the way...just my thoughts, but when your number is called, doesn't matter how much body armor you wear, its your day, its you day. It wasn't my day, when we hit an IED in Iraq and it wasn't my day, when my chute got fouled up in the early 80's.
Have a blessed day.