All the hulls are generic. You can fit a colony ship on a cruiser hull if you pack lightly.
Colony module, bridge, three supply tanks, three large engines, and enough basic crew quarters and lifesupport to satisfy the requirements should *just* fit, and will give 3.5 speed (rounds down to 3)
That's the price you pay for cheaping out on the hull
Using medium or small engines should let you eke out another speed point.
The thing to keep in mind, is that those scouts are only 50% more tonnage than a large fighter...
They're basically mobile, warp capable, maintenance costing fighters.
Missiles have 5 areas, but 7 missile types.
Direct fire has 4 areas, and 4 weapon types.
Its not so crazy if you think of it that way
Ships all start with range 1 sensors built in. Researching sensors allows you to boost that to range 2 (basic sensor array) or range 3 (large sensor array), and more with tech.
Legacy facilities are uberfacilities that are only seen on homeworlds, and can not be built in-game. It gives full sensor coverage of the homesystem.