before i do anything hasty...if you tell one to leave you alone for a bit, can you get them back?...and of so, are they in the place you found them originally?

I've read posts where people have left characters in houses and then came back to fetch them much later without an issue. I left my companions outside while I went through an entire building once and fetched them without any problems. Basically, yes. Without having tested or confirmed all conditions (leaving them outside a death claw spawn point for 5 years in game time kind of stuff), can't say for 100% sure there won't ever be issues but off of base knowledge it won't be a problem.

I know you can leave them somewhere, i have ede and boone holed up in novac...but you cant invite anoher companion unless you get rid of one...or am I just not able to do this yet?...I want to give the other guys a go but i dont want to loose boone forever by choosing the chat option to leave me alone

You can dismiss them to the Lucky 38 and recover them at any time.

I've not had any issues with companions going missing. I suppose, however, if you tell them to WAIT somewhere (IE, no dismissing just making them stand still) they can run off after enemies and you won't know where to find them. So I suggest if you need to leave them behind for an extended period of time, tell them to go to the Lucky 38.

Iv not reached lucky 38 yet so Il wait til I have, thanks dude

Before I reached Lucky 38 I dismissed Boone and he ended up back where I found him.