1. Agonizers ignore standard marine save. Venom blades have poison, wich is harder to get RR with now in 7ed.
Other then that most other CC (power)weapons we have either have AP3 or better or poison.
2. not played much aginst drop pod flamers, besides our transport have always been a bit like lotto
and our units seldom have a good save so... well we have Feel No Pain for a reason
3. Feel No Pain helps, but usually its more a thing of killing the enemy before he kills you. be agressive and divide and conquer. oh and Btw suicide attacks is not always as bad as you think shooty armies do not like being stuck in CC or if you go where he can't get you but you can concentrate on 1 unit a time.
4. Venoms are good for dakka support with the units of you choice in it, small CC squad, small AT squad or just more dakka squad. Venoms only really need the extra splinter cannoon upgrade.
Raiders for anything else,
best upgrades for raiders are,
Flicker field/ nightshield or both depending on the purpose of the unit or your play style or if you have ponts to spare,
Grisly trophies for the Ld reroll your CC units really want that because you do not want them to run when the enemy get the next turn due to our amphetamine parrotty save
Splinter Racks for dakka boats.
and last don't afraid our weak little fragile units can kill bigger monster then you think , like a wych with an agonizer killing a really bad ass combat monster IC in challenge
just keep rollling 4+ on that save