Hi Willow2, you may want to keep a PC (with regret) for those rare times you need it for some Web site which won't play ball with your Mac, or if you need to test some Windows-only software, or to give to a child to destroy.
Am really glad your dh is keen to move to Mac at home. It's so nice not to spend weekends fixing spyware damage / and faffing around with sick Windows boxes.
In a virtual community you should be suspicious, but I suspect that if someone can supply a receipt / cc statement to support a purchase, and that they've spent x months posting 'normal' stuff, that they aren't about to rip you off / sell dodgy goods or otherwise do anything unpleasant.
Ref: Would I still be pushing Mac if I wasn't selling mine ? Can only suggest you search archives for user hub2dee and word Apple or Mac and you'll see I'm often suggesting they are the remedy to all the world's ills.
I haven't advertised my laptop anywhere nor mentioned it might be for sale elsewhere on MN, but when you said you were considering the 15, I thought a secondhand 17 might be even more suitable (esp. if you spend all day infront of a screen) and cheaper.
If you buy yours new, you may want to consider Applecare. It's a 3 year software / hardware telephone support / parts / labour warranty. Possibly your household contents insurance would cover accidental damage anyway...
I'm in North London, but don't tell anyone. It will be our little secret.
Ref: Mac Mini - haven't you looked at the Apple web site yet ???? It's their newest computer - a little box the size of a couple of paperbacks. Very nifty and fairly inexpensive. Attach it to any existing keyboard / mouse / screen (for example your ex PC bits) and ta da ! OS X on the cheap !