I have a laptop, and am told that I can get a sequencer for the laptop that will run rings around any onboard seq. I don't want to be limited to preset sounds, I want to be able to program loops to one key. I want to be able to load any sounds I want. What do I need?

The sequencer is a seperate question than the others. If you already have a laptop don't waste your money on a built in. A built in sequencer will do very basic editing and a limited number of tracks. Software will allow you to do any kind of editing, see what you are doing on your monitor, cut and paste a section, loop, have sheet music where you can manipulate each note and add any controller (ie., graph volume, pan, modulation, etc.) and about a million other things that a built in sequencer will not. There is no camparison. You will also save hundreds of dollars. go to www.cakewalk.com and download their demo. You can use your soundcard to check it out. The demo will probably not allow you to do alot so just expect that and don't get frustated thinking it is a bad program. It's about the most popular. You can find CW used for next to nothing at www.harmon-central.com
Maybe if you told me what you mean by preset sounds I could answer that better. You will find new preset sounds for most synths for free here at Synthzone. I can't comment about your other questions. They are more synth specific and not software specific even though there is software that allows you to do these things.