Using a time machine to back up iMac

[steveatesh]

Awaiting delivery if a new imac with 1 Tb fusion drive, and I'm trying to get everything in I need to so ready to go.
It's my first Mac so feeling my way a little.
The latest thing to raise it's head is back up for the imac.

My PC currently has an additional internal 500gig SATA drive and an external 500gig SATA drive , plus a Buffalo Duo NAS, 500gig made of two discs set up as RAID 1.

I understand the iMac has USB 3 ports so I will have to change how I connect an external drive, assuming it's still relevant for backup.

I have read that Time machine will only work on an external USB drive that is larger than the internal drive, none of mine are that large so I'd have to buy another hard drive if that is correct.

So questions please.:
1 is it correct that Time machine can only be used with an external drive that is larger than the fitted internal drive on the iMac?
2 will I still be able to use the NAS in its current setup - ie 500gig. RAID ?
3 if I get another external drive (1Tb?) is it best to get one with a,power adaptor so I am not drawing power through the iMac USB connector?
4 if I use Time machine will it give me full control over what and when back ups are made, down to a folder level?

Sorry if these are basic questions, I don't want to do anything that risks the Imac being damaged and can't afford a Time Capsule in the immediate future!

Thanks in anticipation.

[steveatesh]

Right thanks everybody I'll get a powered USB case and slot the current 500gig SATA drive in it (it's still bare).

I'll use that with TM and see how i can best use the NAS when it's all here and running.