If you save-scum a bit for good Entrance placement and few blocked segments, every base you own can fit at least 3 large hangers, have both a Missile and a Laser battery, and still hold either serve as as a research or production base. Your initial base, which is guaranteed to have zero blocked segments, can do everything at once.
Here's how it works. For your initial base, try to get an entrance that's as far from the center as possible, and set in the middle of one of the base's four walls.
Both of these layouts allow for at least 1 square of blocked space (2 if you omit a laboratory, 3-4 if you omit the defensive weapons as well), and the only parts you really can't move are the Workshop, Alien Containment, and Hangars. It will support 10 workers, 10 scientists, 4 pilots (for your dropship and favorite 3 interceptors), and up to 12 soldiers. The only problem is that storage space will be at a premium - don't keep
any equipment your squad doesn't use regularly (or, optionally, omit the lab or a defensive structure to add a Storage space).
Both of these layouts are defensively strong (enemies have to go through at least one nonvital structure to get to anything important, giving you time to react) and have an empty space near the Power Plant; that's intended to house the Antimatter Storage facility once it's unlocked via research.
It's very important for your satisfaction ratings that every base you own has detection, interception and troop deployment capability. UFOs can show up anywhere, and you want to shoot them down and recover them as soon as you spot them. Once you've got multiple bases, it's okay to devote one to research (remove any workshops in it for extra laboratories) and use the rest as production bases (remove the laboratory for more storage space, or remove the laboratory and a defensive structure and do some reorganization to add a second Workshop).
I typically put a base on every major continent; North America (around Wichita, Kansas, 'cuz Roswell isn't central enough), South America (a little northwest of BrasÃlia), Asia (Ulaanbataar), Africa (Central Chad), and Antarctica (South Pole). To cover the gaps, I place Radar Towers in north-central Australia, South Africa (making sure it covers Madagascar), the eastern peninsula of Russia (in the middle of nowhere due south of Leningradsky), and the middle of Iceland.
This gives me pretty much worldwide radar coverage. Since UFOs can't land or do anything on water, they can't roam overland without being spotted, and I have interceptors that can reach any point my radar can cover, they're pretty much outta luck. My UFO Hangar usually goes next to my biggest production base; the closer a UFO Hangar is to the base that's doing its disassembly, the faster the UFO gets taken apart. I'm not sure if that applies to research as well. If it does, I'll establish a second Hangar next to my biggest research base; the UFO goes there for research and then gets transferred to the production hangar for disassembly.