Should I stop accepting/sending bitcoins in days before / after forking, or wait some more confirmations more than 3-6 ?
If you only care about BTC, it shouldn't matter. There is supposed to be replay protection for Bitcoin Gold, but even if there isn't, you only risk losing Bitcoin Gold by transacting normally with BTC.
The real risk in these forks (if they have no replay protection) is in trying to send the forked coins. Many users will likely get those transactions "replayed" on the original chain, and if the funds are sent to an address they don't control, they will be lost.
I hope that in the future we have more simplistic coin splitting tools to make it easy for users to dump their altcoins without putting their BTC at risk. At least, I hope to see RBF and nLocktime become more intuitive for users, so they don't have to depend on exchanges/third party services to split coins for them.
If you do care about BTC, then it is your duty to access the coins that are given to you in a fork and basically dump them on sight.
So first of all control your private keys and forget about exchanges. Just wait for segwit2x to happen, then move your coins to another wallet, then use this empty wallet to access segwit2x and BGold coins and dump them.
We must crush the prices of forks and our weapons are the free coins that are given to us on forks, this is how we strengthen the real BTC, and we get free BTC in the process doing so.