1) If you're doing a cam at the same time I would recommend you pull the motor. A cam install takes 30 minutes tops with the motor out. Plus I know torquing head bolts with the motor on a stand is much easier (especially the rear head). Removing the motor is a 3-6 hr job depending on your knowledge and mechanical ability. I started Friday at 3 pm and it was out by 7:30 or so... having someone who may have done it before to help is a big part of it. Mainly just making sure you've disconnected everything, undone all bolts, etc.
2) I paid $620 shipped for all the hard parts for my top swap. For the cam go XP ($300). For all gaskets, fluids, and misc trips to the parts store I would plan on another $300 or so
3) If you're fairly mechanical, nothing. It's just time consuming and making sure you do everything exactly right (correct torque specs, having all the right tools, etc)
4) Once the motor is out, I would leave a solid weekend. Mine took about 28 working hours spread over 4 days. If I wanted to, I could've had it done in a weekend, but I took plenty of meal breaks, sleep breaks etc to make sure I didnt go crazy.
5)
Parts : Junkyard would be nice, but most of that stuff is very hard to find. Late model cars get picked over pretty fast at least around here. I would say Morad, although I did have some problems with some of the stuff he sent me (bad sensors, missing bolts & brackets), his prices/service/shipping is bar none.
Gaskets/Belts/Fluids/Misc : ZZP/GM dealer/parts store... most can be had from parts stores but I found there are some gaskets that nowhere but GM had
Hope that helps! Any more questions, feel free to PM me.