You are on the right track already! Being observant and paying attention to detail is key to scouting out a good carp water. IE: bottom composition, vegetation, etc. You are probably correct in regards to the spawn. When they are spawning they have only one thing on their mind, and will blatently ignore most offerings and baits during this period. I don't know exactly what the criteria is to trigger the spawn, but obviously temp is a huge factor. It's usually quite obvious when carp are spawning as they will individually, or in pairs cruise the shallows and shorelines splashing and rolling as they prepare. Typically spawn occurs around April in N. Illinois. When carp slurp at the surface, they are feeding on food source of whatever kind...insects, seeds, etc. Carp can be very finicky or very gluttonous depending on their mood. In early spring I would suggest only light baiting and smaller hookbaits. As the temps rise and the fish's metabolism increases, then more aggressive baiting and larger baits could be used. I would suggest starting in one of the shallow bay areas where you've seen fish group. Each water is different and thus trial and error will tell, but I' ve fished waters where the carp were seen grouped and cruising, but impossible to catch fish in those spots. Where the carp group isnt always where they feed, but definitely a good place to start...just something to think about. I believe barometric pressures and temps have a large effect on where the fish will be(shallow or deep. cover or open water) You will get the feel for what works best for you and when. In regards to baits, there are 2 basic types. 1) Short term(corn, maize, worms, etc.) these baits offer instant attraction qualities and are the best choice for fishing new waters. 2) Long term(boilies, etc.) These baits sometimes require a bit of training the carp to accept them. If you have a fairly clean bottom, bottom baits could be the best bet, but if you have debris or weeds on the bottom, a popup(floating bait)fished just above the weeds may be the best bet. A small piece of yellow foam cut into a corn shape along with 1-2 kernals of corn is a quick way to make a boyant or semi-boyant popup. Size 8 hook is a good starting point. Here is a couple links on prebaiting
www.carp-usa.info/carp-fishing-forum/30-...r/98-prebaiting.html
www.carp-usa.info/carp-fishing-forum/30-...ebaiting-part-2.html
Here is a cool article on understanding carp
www.carp-usa.info/carp-fishing-forum/36-...erstanding-carp.html
There are also some very good video tutorials in the video section.
I hope I covered all your questions...I'm sure theres something I forgot, lol...If so, just let me know.