Two questions about acitivities I couldn't figure out .. any hint appreciated

a) Is it possible to have different taskbars for each activity?

b) Is it possible to have a selected set of applications automatically start when I switch to an activity?

Regarding a), it's not possible. It's technically doable, but someone needs to write the actual code.
Regarding b), you can do that if you play with sessions, saving your session with the activity stopped and once you return to it, starting it would restore the applications you had there. If you mean "all the time" instead, it's only possible on first run, when you create it and switch to it, using an activity template (some are shipped by default, e.g. Photo activity and similar things).