Hrm, quite a list of questions. I'll answer generally rather than specificly, as you seem to be looking for an overview.
Master of orion tends to play out in a fairly predictable 4 phases: Land Grab, Consolidation, Survival until fleet capable, War. There's chances to win the game outright through each phase, but that's generally how the game goes for a human player.
The first phase is a land grab. You do anything you can to get more planets. It's really important to get your fair share of planets at the beginning, as a small empire has an enormously more difficult time crawling back into the game compared to an average size empire.
Highlights of the land grab:
Propulsion, Planetology, Construction technologies are usually prioritized.
You build a lot of scouts to orbit planets - it's generally better to build a scout for every planet, than to use a single scout to scout more than one world (as a scout can chase off early AI Colony ships and scouts).
You may get some milage out of the Long Range Lemon - a medium hull equipped with 2 regular lasers and reserve fuel tanks - or a stack of popgun fighters (small with 1 laser, and a shield if you can get it) depending on your geography. The idea is to hold early stars against the early skirmish fleets of the AI so that you can settle them.
You have to be unafraid to fight for planets that you view to be strategically important, and you should embrace the philosophy of the weed. Be greedy. Spread like a virus. Let the AI tell you when to stop (it'll be obvious when stops you).
Phase two is consolidation. Assuming phase one went well, you'll now have from 4 to 18 worlds. Some of them, like your homeworld and second planet, are probably doing reasonably well. Others are far behind. You need to get them all up to speed, and you need to establish a solid defense. Generally this is where I swap over to an equalized technology budget (focusing on techs that improve my missile bases to start). The key concept here is to stand up your frontier (whatever it may be) and start cranking out missile bases. As you play you'll get an idea of how many missile bases is enough to deter current AI fleets. For now - assume you need more than you think you do on the perimiter, and slack on your back lines. Please note that no planet in your empire should have 0 bases at the end of this phase. You want to get your missiles on the cheap where possible by having bases in place before you get shield, missile, armor upgrades to make them more expensive.
During phase two, you've probably had a few "brush wars" or even a cold/hot war. The AI will test you, and you may or may not have been able to turn them back. Phase 3 consists of the long winter of superior AI Fleets and technology. You're going to have to hold on long enough to research, steal, trade, or luck your way into a successful starfleet technology. I don't consider going on a galaxyquest until I have a few key technologies (as a rule of thumb. In my latest game, armed with 2 fertile planets at the start as the bullrathi I waged a war of "buy a bear and send him to a friend" on nuc bombs, lasers, and luck against a coid - but that's for another discussion). Here's my shopping list for "fleet that won't get smashed arbitrarily while transports are en route"
I want a beam - ion cannons or better.
I want an engine - sub light or better (fusion is ideal).
I want a bomb - fusion or better.
I'm willing to use other technologies as they are available, but my usual "end of phase 3" indicator is that I have fusion bombs on a small, with fusion drives, and perhaps an inertial stabilizer. At that point you can glass most enemy planets.
Phase 4: War. The goal of phase 4 is really phase 1 in disguise. We want to achieve some extra land, and most importantly - use this period to aquire crucial missing technologies with the best researchers in MOO. The pointy sticked sort.
If left to my own devices, I often find myself picking a choice target as my "soon to be invaded" target, and rather than focusing on it immediately, I'll send my fleet to glass anything nearby it that I'm not interested in. Then I'll invade the world of choice. Which world is the right world will change based on your tech vs your opponents, but generally you want something around size 40-60. While larger worlds are larger prizes, a base 40-60 can support a surprising amount of factories, and the AI tends to underbuild missile bases, so they're a bit softer than avg.
Once you've aquired technological parity through a series of strategic invasions, you'll want to start seeing about holding what you take. Between bases/reserves and a repulsor or strong beamship, you should be able to take a single world and hold it. Generally when that starts happening, you're winning.
There's a lot that can go differently, of course, and you'll have to adapt to it as it comes - but the general pattern tends to hold in most of my games.
