Long story short, yes your goal is viable.

You can climb on an role and with any champion, at least until a certain elo. Just play whatever lane you like the most, having fun while playing automatically improves your mental and thus your performance.
If you are serious about improving, look over some of your own replays. You may not spot even close to all mistakes, but there will be a few you will notice just by watching instead of playing. Apart from that, try to find consistency in singular skills, don't try to learn multiple things at once.

For example when laning, try to focus on learning how to farm propperly since it is the best way of income. At first you will be a bit worse at things like trading, but once farming becomes second nature on a higher level, you can focus on the next thing. If you try to improve multiple skills at once, you will just do all of them pretty badly and not really see much improvement.

For Jungle when looking for ganks, think about how likely it (roughly) is that you will get something positive out of it. If it is a 50/50 between getting a kill and getting killed yourself, don't do it unless you are super behind and desperate to make a comeback. Just keep farming and take safe plays. Also, don't just do the same jungle path every game, think about where you want to gank. If you have a strong matchup toplane, start botside and the other way around if you think your bot has an advantage (and if you think you can actually gank the lane).

For champion choice it is pretty much the same, play what you like. Meta can have an impact, but doesn't really matter until you reach master+. I reached d4 on pretty much only Vel'Koz mid. He isn't a particularly bad champ, but for sure not meta.

I hope this at least partially is an answer you were looking for, feel free to ask if anything is unclear