I main Caitlyn and also enjoy playing Heimerdinger, morgana, Kog'maw and Janna.
Im looking into buying a mage (to escape the bot lane a bit tbh XD)
and I wanted help in choosing between the following mages.
I want a champ thats not too difficult and has an escape and finish sort of like caits net and ulti. Help me out homies.
Of the list you provided Ahri is the closest thing you want, but she doesn't have a great finisher. To be honest i think Le blanc would fit you better, her combo is preety easy can 1 shot people at level 6, while being quite safe.
Karthus is great because he just needs to chill and last hit propel with ult. He's great at tilting like a yasuo who wants to fight all the time and you can just pop him down with q all laning.
People say Karthus is useless and is only good because of his passive - which is wrong..He just doesn't have an escape. You should give him a try. Anivia is also a really good choice, if you like heimerdinger try Zyra, instead of turrets you use seeds.
Oooh, I would go for Ahri because I adore her and she has so much escape potential, but I'm going to be nice and vote for Brand who I think has a close enough kit to Caitlyn, possibly even Anivia. Both have a stun, though one is slow and very awkward while the other you have to chain with a Pillar and fire shot thing.
Karthus might be hard as you have to realize his Q is a delay cast which throws off a lot of people. Xerath you have to be extremely good with skillshots, especially his ult which is about the same size as the character model.
I think based on the champs you mentioned you would like xerath
