what top 1-5 coins of each of the sectors would you recommend ? which have a good background and solid fundamentals ? would you go for 1-2 top coins with big martket cap and 2-3 with lower marketcap ?
I can't outright recommend you some potential altcoin - but you should do your own analysis instead of expecting the community to do it for you. The Top 10 is a good choice in my opinion - but it may not suit your tastes and desires. Some users tend to choose lower price options like XRP, ADA and a few others - but I'm not sure which coin catches your eye.
what would be the best time to start buying them ? now ore before halfing ore after halving ? some of them are really low how low can they even get ?
Before altcoin season arrives.
what do you think if the ETF would dissalow BTC how would this impact ALTCOINS ? how badly would they fall ?
Depends on how strong bitcoin gets other fundamentals. ETFs are just one good fundamental - but the halving could also push the price of bitcoin more expensive and the impact will be felt on altcoins too. If bitcoin price corrects - altcoin prices tend to correct too.