Certainly move this thread to the Spider forum.
What you ask for is certainly possible. I usually use drums only to get a tempo; You need to get used to the interface. You can do it without the drums, but then the timing is all on you - with the drums, the loop seems to restart on the beat so the loop sounds better.
To use the Express for start/stop you need to set the mode - each time you power cycle the amp. The amp forgets this setting when you power off.
To change the tone, record your first layer, stop recording (loop can continue to play) change the tone using the controls or foot switch, then record your next layer, repeat as desired.
Spider Jam is an excellent amp with a lot of great tones and easy to use features. Takes a little getting used to but overall, a great piece of equipment.
One word of caution: I bought the Spider Jam several years ago. Since then I've purchased a ton of Line6 products including a dream rig. I still use the spider jam on a regular basis in my home rehearsal studio.