A few general questions I couldn't work out from online strategy guides

[dgg9879]

I am playing on easy mode.

Played the game once but found it hard even after reading the manual so now replaying after reading strategy guides but still find it a bit daunting.

Please answer these questions for me if you can.

What year/strength level should I start attacking dominators (if I start too early I'll be killed if I start too late they'll be too strong)?

One strategy guide suggested using Scientific Bases to upgrade equipment rather than buying more expensive equipment because the more expensive equipment costs so much more to repair. But the optimum hull is supposed to be 800 to 1000 in size. Should I wait until I have a hull this size before upgrading it at the Scientific Base or upgrade my current one (450 in size).

Is there an easy way to keep track of which planets I've "probed" rather than writing it down?

I believe you are offered RTS missions at planets. Is this prompted by killing all the Dominators in a sector? How does it all work? I know you kill Dominators to get parts that are taken to Science stations to do research to destroy the Domintors. But how do the RTS battles fit in? Is that what you need to do to liberate a planet?