Hello my friend,
I am not the most experienced of players but I need something helping me to procrastinate. Well - lets see: problematic starting position, weak stars…
Since this is a multiplayer game and you had, as you said, a weak starting position, there is no guaranteed path to victory. But as you say, terraforming helps closing the gap.
So if my starting position were exceptionally weak I would go experimentation(highscaling)/manufactoring(defensive military power)/terraforming(good for bad stars)/banking(starvalue does not matter) . Defend until terra … 8 and only attack if losses were absolutely low.
u said u have ur enemy A, one behind that one B and two behind B: C and D.
If the player in my enemies back(B) would not be willing to fight him I would try to support exactly one of C and D until that one destroys B and becomes a possible ally against A. How to support? Techs and money, since your money might be more efficient on the star systems of B than on your own ones.
Trade Scanning enabled? Np, then I have more tech-tradepartners than my enemy and will outrun his science without even spending much money on it.
just some thoughts,