Just search league of legends', and clash of clans' ranking systems if you can't understand what I am saying/trying to say in a simple way.

Not entirely sure how elo works in league, but I heard it is similar to clash

Clash: you are in leagues, and depending on how many stars you get against someone else's village you get certain amount of trophies(also based on opponent's town hall level/league)

You need a certain amount of trophies for each league, and rank up/fall according to your trophy count.

You can't "selective spar" against another town hall, but you could get lucky and find an opponent with low defenses/a lot of resources, but you would need to fall down to trophy range of 900-1200 to find inactive town halls with lots of resources in pumps. Other wise the higher your trophy count is, the more active people are, so less gold "less ez wins"