As far as I know, you can only power up the sail (over trim) it so much until it looses its curve that produces the lift to move you forward, then all you get is a 650 sq ft weathervane.
Telltales on the
jib require a little bit of know-how on how to use, much more so than on the trailing edge of the main, IMHO. That is why I said it is easy and hard at the same time, because once I thought I knew how to read the main, along comes the
jib and they lift at different points, some fly backwards, some point down, and it all means something. If you can get them to all point back without more than sheet tension changes, you're in good.
As far as the boom to centerline, do some reading up on the post here about how to use the traveller, it explains more than I would be able to about upwind sailing and wind speed.
For me, when I was (and I STILL am) learning to sail, I stuck to the KISS principal and just kept the traveller on the centerline and practiced on things like trimming in and out to watch the telltales change. It is a neat feeling to be able to lock in the sheets to cam
cleats and just hang out while the boat sails itself on a good balance after you learn how not to fiddle too much and get a quick, good trim.