It all depends on what kind of youtube channel you're going to have. If you have a Gaming channel, and let's say it's PC gaming, you're going to need some RAM. I'd say 8 GB would be a suitable amount.

But, what you need no matter what, is plenty of memory. 500 Gigs would be a good amount. High Quality videos can be consuming if you have a small amount of memory. You want a good processor as well, other wise your computer will lag A LOT during recording.

You'll want a good video editing Software (I recommend, since you're getting a Mac, iVideo.)

I don't know about a Mic. I don't have a good one. Just a built in one (Which mostly all of them suck).

All in all, go for the type of computer that can store plenty of memory, and at the same time has a good processor.

Edit: Also, for a recording software, I use Debut video software, it's free, and it gets the job done. It has it's limits, but oh well. The best are always pricy though. :p

Mac is a great computer but it has its down sides.

If your going for a console type gaming channel where your just posting gameplay from xbox or ps3 then a mac is pretty good

I would go with a elgato game capture HD! hands down best HD cap card!

For a mic the built in one is good but a blue snowball or blue yeti is probably your best choice!

Editing software is pricey but my parents work at a company that gets all adobe products fee so i did happen to get after effects and Premiere Pro Which are great software but even still i go back to iMovie because of how easy it is to use. I mean it's all preference if you ask me.

Best software for video editing: Sony Vegas Pro 12

Best software for GFX (thumbnails): Adobe Photoshop cs6

The best cheap capture cards: [ Register or Signin to view external links. ] or [ Register or Signin to view external links. ]