The "bug" is fixed by building another forge in a system that has an open void. If there are none available then there must be very poor planning on the players part or a concentrated effort mid to late game amongst the other players.

Hoping very strongly for Tau faction. Not because it's my favorite faction (maybe third or fourth favorite faction), but because a friend of mine is an avid Tau fanatic and with the inclusion of that faction I know I could get her to play anytime =D
 
Tyranids and Necrons are my top picks for new factions, but I'd rather have Tau over them for her sake.

As I'm not yet experienced enough to speak intelligently on questions 1 and 3, I'm only going to adress question 2.
 
The only race I'd like to see added to the game are Tyranids.
 - I'm make their game pieces purple.
 - I'd give them a massive pool of tier 0 troops, with plenty of ways to get them into play fast and cheap.
 - I'd give them a very limited pool of tiers 1+.
 - I'd have combat cards key on higher-tier troops to grant bonuses to tier 0 troops to reflect synposis.
 - I'd give them ways to easily generate tons and tons of reinforcement tokens.
 - With so many ways to generate cheap or free tier 0 troops and reinforcment tokens, I'd consider having them be automatically destroyed if routed.
 - I'd consider giving them an alterante win condition (such as take over any four planets containing an opponet's buildings) if it could at all be balanced.

Yeah, I think 3 players involve some balance issues around the politics...and my sense so far is that most of those have to do with early game set-up. I'm curious: in your 3 player game, did you have someone stuck in a corner?

We've got a simple house rule that works pretty elegantly with the games rules to produce a 3 player map that is reasonably fair and, I think, discourages teaming up like that to a degree. I wonder if it is helpful in your group We say you can't set home systems next to each other, unless there is no other option.

Here's some of the reasoning:

https://boardgamegeek.com/article/20101646#20101646

To the analysis here, I'd add that having a secure home system in a corner without objective tokens is nice. But so is having a system that is farther from the other two players. The benefits here include the possibility of having a relatively safe place to put cities. The last 3 player game I played, the early capture of a city made a pretty huge difference...

I've played 3 player games more than any other and it definitely makes politics a more important part of the game. I don't think they're unbalanced however unless its 2v1 the entire time.

One observation about the Triad problem: the race in the middle tend to suffer, basically because ypu can't rely on corners to avoid being blind-sided. Those who start on a corner of the board can move the frontline without being worried too much of defending the most remote systems.