My current game is, let me do that math, 66 years in. My usual expansion is best described as slow and thorough; in each system I aim for a nexus world with nearly identical atmosphere to Earth (not just for RP reasons, as having at least 1.0 atm also protects from beams), large population and a variety of installations, and, wherever possible, in system mining colonies mass drivering every type of mineral to the planet. Basically every planet is fully self sufficient and capable of handling its own expansion if all the others were to get wiped out.
I also normally only colonize one planet in each system, including Sol; while I realize the trade benefits to multiple worlds I like the centralization; it makes defense easier and things easier to keep track of.
Currently I've got Earth with 1.78b pop, Eden with 251m, Shangri-la with 147m, and Avalon with 81m. My military is split between two groups (previously three, before I scrapped the survey wing because they were outstripping my expansion rate); a planetary defense group of missile bases and FAC squadrons, and a naval fleet of 34,000 ton battleships and 14,000 ton cruisers, exclusively beam armed. All told there are 11 missile bases, 60 FACs, 5 Battleships, and 8 Cruisers. I previously used a science ship variant on the 34,000 ton battleship for survey duties (had four, and even with a jump drive and survey sensors they were quite dangerous) which in theory would have aided the fleet in times of war. Unfortunately they never ran into any enemies so I didn't get to test them. They were called the Galaxy class and inspired by Star Trek
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Which on a related note, is kind of why I lost interest in that game; I built so much but there weren't any enemies to provide challenge.