1. My favorite games are both homebrew games. Vectrexians and Vector Pilot. I also enjoy Berzerk a lot. Clean Sweep is pretty good if you enjoy Pac-Man.
2. Personally, Fortress of Narzod never seemed to be enjoyable, maybe I need to read up on it more and give it a chance though.
3. here's a =3635§ion[]=1&mode=Search&title=&Mfr=&Released=&Developer=&Designer=&Scarcity=&Dollars=&PartNo=]LINK to a DP price/rarity guide. I assume Polar Rescue and Pole Position are likely candidates for most rare (besides Minestorm II)
4. Generally, loose carts are $15 and up. loose carts are fine but IMO they lose appeal without an Overlay. I know someone was making reproduction overlays but I don't have any info on that.
5. I own this one and it works fine, though mine doesn't have a cart shell. I bet there is others but i'm not sure.