Total newbie here!

Hey hi and welcome to the forums!
Monster high is quite a good start before you went for the bjds indeed!
As your now entering the bjd zone I would just recommend the doll you really like and not just buy one because it's only cheap (all tho if you just happen to find a cheaper bjd beautiful, just go right ahead xD).
As for clothing compatibility, it depends on what kind of genre of clothes you like also. However minifees for example are a little slimmer then other msd's, so while buying clothing you just have to be a little more aware of the measurements. Since they are quite populair tho you can find a ton of clothing on etsy for them

 

Welcome to the hobby!!

Resinsoul Mei is the ultimate starter doll, I think. She's got a sweet face, and she's (relatively) inexpensive. But she's very slender, especially if you get her on her own body.
I have Resinsoul Lan (see my avatar) on that particular body, and most regular clothes are a bit too large for her. I have a Bobobie head on Resinsoul Rong body, which is double jointed and slightly chunkier. It's not too difficult to get Mei on a Rong body if you'd prefer double-jointed.
Shoes are problematic for all Resinsoul girls, because their feet are narrow. It depends on the style you want, too.

I think MiniFee is the easiest to shop for. There are tons of MiniFee clothes and shoes on Etsy. MiniFee is a bit shorter and chunkier than the Resinsoul double-jointed bodies. I've used MiniFee clothes for my girl on the RS Rong body. Sometimes they need a bit of a tuck, sometimes they're just fine. (MiniFee has a bigger waist.)
MiniFee is slimmer than most MSD dolls, but Resinsoul dolls are even slimmer.

I don't know about Momoni - I haven't seen any of their dolls in person, and currently they only have out-of-stock 27 cm dolls on their website, which is a totally different size. They look like they might fit some Barbie clothes - but not pants, as they have bigger hips than Barbie.

I hope this helps.

 

My first was a Mystic Kids Lillian (my avatar) who I still ADORE! Her body is one of my very faves! She was a great price and came well-strung and easy to pose. My most recent acquisition is a DollZone body and it is my absolute fave right now - it just bumped my Lillian out of first place. Well-strung, super poseable, graceful sculpt, pleasant new-resin squeak ^_^ Like seriously, I want a whole army of these! Or at least one more, LOL! I'm waiting on a ResinSoul Lan (or is it Ian, I can never quite tell) head for her. Can't wait! I haven't had a resinsoul body, but they really look lovely to me.

I can't speak to clothing fits very well, because so far I've made everything mine have with the exception of some items form a fukubukuro from DollHeart. I think MSDs in general should be decent to buy for, but I'm not really sure.