1- as I understood that bitcoin mining is becoming less profitable every day, unless you have a massive hash power, I'd like to try mining altcoins, but am I wrong thinking this is profitable ?
Altcoin mining is actually profitable but I don't suggest joining until the middle of August as there is a lot of turbulence in prices because of some stuff in bitcoins (I just don't wanna go into details since you're new)
2- following that, are there ASIC miners (I only see those for bitcoins, unless antminers are also able to mine altcoins?)
GPUs are used in altcoin mining (ethereum, zcash etc.) ASICs are only currently available for bitcoins and litecoins (thank god )
3- last one, when scouting for a pool, would you recommend a pool/software that mines a bit of everything or a pool for each cryptocurrency I mine.
There's no such thing as a pool for everything. You choose a pool for every currency you mine (and it's not that big of a deal).
Here's what I use when I mine the following.
Ethereum - ethermine.org
Zcash - zcash.flypool.org
Decred - dcr.suprnova.cc
Lbry - lbry.suprnova.cc