Thanks for all your replies, some where very helpful !

Some altcoins that have been mentioned have been on my watchlist as well like STRAT, OMG, WAVES...

I'm sure XMR and ZEC are also nice to invest, but I don't wanna change some parts of my 80% BTC/ETH/LTC portfolio to them.
Smaller cap coin portfolio should stay around 20%, I think I'll mix it up like this :

50 % BTC
15 % ETH
15 % LTC

5 % IOTA
4 % NEO
4 % STRAT
3 % WAVES
2 % OMG
2 % QTUM

I took out XRP and XVG, I'm anyway not really sure about the future of these coins.
I still believe IOTA with their blockchain-free tangle technology will be successful.