RE: First thermal?
When climbing under power you are looking for max climb rate. Staight up only works for hotliners, most will need a less sever angle. Practice will tell you MUCH more than I.
Maintaineing adequate air speed is important. Forward motion lets the wing generate lift. this counts in thermals and under power.
When flying a new plane we often allow it to float or fly very slowly. Lift can hold the plane even sometimes but flying a circle with adequate speed lets the plane's speed work along with the lift for maximum results.
I thought BMatthews was quite excellent with his above post, well done!