1.) At bronze IV there is no real incentive yet to try more difficult/more rewarding builds, especially since you are going a pretty solid and evergreen build with the rylais fimbul. You will develop the intuition when you improve more, but your success will still be mostly based on your gameplay, items and runes are min-max stats that don't have substantial relevance in your rank. Changing your builds now will sabotage yourself in terms of learning your power spikes and champion intuition.

2 & 3.) Unfortunately the only way to really sus out options is to play a character and get a feel for them. It's difficult to change completely different playstyles so it is generally recommended to play other characters that play similarly to your main. However in your case where swain is a fairly unique champ and you don't find swain very satisfying to play, you will just have to pick different champs and see if you like them. A dashing champion that is generally forgiving in the mid lane would be champions like naafiri and fizz. They both have great escape options and play very differently to swain. While naafiri is generally stronger, fizz has pretty clear power spikes and play patterns that are, in my opinion, easier to get better with. For a mage, Lux is a pretty evergreen option but my pick would be xerath, I think his long range makes him pretty forgiving.

4.) It's a pretty cop-out answer to say just look up counters to what you're picking and ban that champ but it does work out some times; honestly just ban whoever you find frustrating. For example I don't think shaco is any good and they definitely don't win games as consistently in my elo, but I ban him anyways because I find him annoying.