I can't answer all of this, but as somebody who plays masochistic - obscene with max AI # on larger galaxies, I personally like a custom civ with super hive as a special bonus to start up factory production nice and early.
The only thing I research is universal communications and I do this with 0% military spend and about 50% social spend (I tweak it so I try and maximise weeks efficiency, so only putting 10% into research for the last week, if it still only requires 1 week). You don't need military spend as you only have 1 or 2 planets, and you're either building social structures or buying ships. I typically look to stop between 5-9 additional colony ships, plus i convert my miner to a colony ship, this being 5-9 * 20 per week costs, and if you go mad you can easily bankrupt yourself.
I use the universal communications to trade with other civs to support my economy, and typically won't break even until maybe 200 weeks. I usually have favourable racial traits for morale so get away with 59% tax in the early game and up to ~ 80% in the late game, depending on other items (I like harmony crystals, but not too early, so you can decide what morality you want to be depending on the balance of power).
I strongly suggest grabbing planets. I usually send my colony ships on slight detours to examine star systems, and look to colonise those closest to my neighbour first - with a few exceptions for those peachy planets. Although you may lose some planets in your sphere of influence, in the long term they will culturally flip to you, so ignore. I never colonise my home systems second planet, or any secondary planet of a small race (I will look to conquer them early, and with their high influence can flip nearby planets later). I will also usually populate 2/3 or 3/4 planets in a system in tighter games, again to in the long term,leaving the 4 or 5 ranked planets to the AI and hoping they'll flip eventually.
Once you've secured your planets look to taper off your ship production and swing into research and social production. You'll need lots of financial buildings, some reproduction buildings can held, and remember to keep trading, both tech and influence, for tech and money.
It's not unheard of for me to overstretch and either become bankrupt or get raped by aggressive early conquests. I typically look to secure economic and then diplomatic techs so that I can play my neighbours off against eachother and put my military development off for a stronger economy. That said, in 90% + of games I secure myself in the early game as a mid-ranked power, and look to tech quickly to larger ship structures and powerful weapons / shields, where I will use my superior influence and maybe the help of an ally to get the upper hand. I'll also be sneaky, for example paying my neighbour to go to war with a race half way across the map, wait 50 turns, and then attack, knowing most of the ships will not be a challenge as they'll be over the overside of the map. I win bout 50% of the games I play.