I have not installed carpet pad yet, but I just ripped the carpet out of my living room, so it won't be long...
I am planning on putting the carpet pad primarily under the floors, but I will use headliner/similar adhesive for other areas as needed.
Dynamat is actually made out of butyl rubber. I usually shy away from roofing materials because they are asphalt (don't us asphalt!) but I see very little wrong with the butyl rubber roll you linked. One thing to keep in mind, it looks like both sides might be sticky, and it doesn't come off very good (at ALL) if you need it too. You could try to use it to stick to your car on one side and the carpet pad on the other side, but I suspect that you may have less than ideal results getting it to adhere to the carpet pad (if you try it, let me know how it goes). Also, it may be thinner than a dynamat type product, which would make it slightly less effective, but lighter (and cheaper)...it just depends on what you are going for.
Carpet should be easy in the CRX. Pull the seats and sill plates and lift the carpet up, one side at a time. If you want to pull the center console you could, but I suspect that significantly more noise is coming through your floorboards. I would not pull the dash because it is a pain in the neck for the small gains you will realize. I work my way up the footwells as far as I can go and call it good, The dash area isn't really a problem spot for noise, at least it wasn't in my s10.
Heat concerns along the firewall...
I take no responsibility for you lighting your car on fire yada yada yada...
I have no concerns at all. Drive it HARD with no carpet in it, you can still put your hand on the floor/firewall and not get burned. When you pull your carpet you will see...carpet padding! If you have any concerns you can put a layer of aluminum-backed butyl down first, then put you OEM carpet padding down (it might(?) be more temperature resistant) then extra carpet padding, then your carpet.
For the fenderwells I would do 20-50% coverage with dynamat/roof seal UNDER the car (it sticks pretty good with proper prep. In the trunk (trunk?...hatch!) I would do 50% dynamat coverage, then 100-200% carpet padding. Under the hood I would do 200-500% dynamat coverage on the shock towers, this won't stop a lot of road noise, but it will significantly dampen rocks/rain hitting the underside of the car.
I'm all for making things out of ABS, but fender liners sound like more trouble then they are worth (at least to me).
https://www.amazon.com/Closed-Neoprene-Sponge-Rubber-Sheet/dp/B00YHT0CNA
Here is a link to some closed cell foam. It is pricey everywhere I can find it. That is why I am planning on using it sparingly where a have to and trying out my free carpet padding everywhere else, all I had to do was buy a house to get it!
If you want to get really crazy (and heavy) look up decoupling mass loaded vinyl, you never come back from that rabbit hole...neither does your wallet
Lizard Skin is also an option, but I have never used it.
Good luck on your dampening. You will notice that your car will be more comfortable and your radio will sound better. You can do a before/after with a free dB meter app, but the numbers will not be as impressive as how good it sounds.
I learned from googling and trying.
Keep learning, let me know if you find something new or awesome
