2 is easy, I do it all the time.
3 should be easy using the streaming audio player
1 should be easy too. If you always do this in a predetermined order, just use setlist mode and use song and song parts. Simple.
If things are more improvised and you are jumping around spontaneously (not planned before), a lot of people do this. If you follow a predetermined order, you can just go back and forth to the next song or medley. But, if it is not predetermined, you might need to set up buttons on a controller and use program changes to go where you want.(There are threads on this topic in this forum. Maybe search “song finder” in the forum).
I suppose ram and memory use could be a factor too. If you have enough ram for what you are loading, you can access any rackspace without any (I guess maybe “virtually any”) and downtime.
If not, you may have to use Predictive Loading, but I am getting a bit ahead of things, I think.
In terms of getting a VTS to try that out, it sounds like you would want some type of rompler, like Xpand2, or Halion 7, or Kontakt, or something from the Korg Collection, etc.
The problem is the way most plug sales work (not GP) is there is a regular premium price, then if you wait around for the big sales, you can get a huge discount.
So for example, XPand 2 (a bit dated rompler, but maybe good for your purposes) seems like it is now selling for $99. But, there are sales that occasionally bring the price way down ($20 or $30, I think).
Hope this helps a bit.
Jeff