There are many reason why I dont like 100% this idea, but I cant focus on all. Two of the most important are the lack of transport because someone is bad at driving/fly or got killed instantly by the bots (rip "trans" by ZSU 23-4 or ZPU) and also counter assets like tanks or IFVs, AAVs.
Why force a guy to play all round only on foot and only use hat kits to counter the enemy assets? Most of the time this is the reason Coop server gets empty so fast.
To balance this you can make the number of enemy assets directly proportional to the number of squads(2-3 tanks or even 4 for 2-3 squads ... bear in mind this is for no counter vehicles for human side) that will be present and you have to take into account that this squad number can vary. Or you can just reduce the size of the map so people are not forced to walk long distances, give the enemy team assets but not more than a tank or 3, but more can be overkill sometimes (same thing as before). Also many other methods can be added to the list, I m sure of this but you would still have at least a backup vehicle in case things take a turn.
All I wrote before, is applied only for maps without respawnable assets. Its ok to have at least 1 or 2 cars to respawn, a logi, a heli- but not necessary if you already have a logi that respawns(or it can be quite the opposite), and if its a map with assets like tanks or apcs, have at least one tow HMMWV respawn after 10-15 min.
You also have to make the map fun, not just balanced, so people enjoy it! Plans are good, problem is they always have a flaw, learnt this by making arma events... Things never work out the way you imagine it to be, improvise!
(wink wink, we know Shahadah first coop version that came with a shit load of assets and almost no counter at the beginning of the round because not all players are so gud at the game and can use HAT) .