I'm going to replace current hose bibbs with rotating gate valves to ball valves.

When I shut off the main line, I think I'm supposed to open a faucets(s). Then start to remove and replace valves.

If this is true, do I open faucets closest to the main line valve? Or furthest away? Do I open valves downstream of the the valve to be replaced? Or upstream?

Not sure what the rule is here.

Typically, domestic water has two loops - one for hot, one for cold. There MAY be four if it's a two story house and the upstairs has separate hot and cold loops.

As long as the valve you open is a cold water valve on the same loop as the bibb(s) you're replacing, it doesn't matter which one. The idea is to release the line pressure.

You'll still get some residual water when you remove the valve, but it should be just a dribble.

I'm assuming you're replacing threaded valves. If they're the type that have to be sweat-soldered onto copper pipe, it's important that you don't have any water near the joint or it won't solder properly due to the heat-sink effect and steam generated when you heat the joint.

Doesn’t matter. But you should replace them with freeze proof faucets if you live anywhere north of Savannah. I did mine with 1/4 turn freezeproof faucets.

Technically speaking, gate valves don't rotate, but rather raise and lower. Ball valves rotate.

I'd suggest buying a book about plumbing like Plumbing 1-2-3 from Home Depot before doing your own repairs.

Thanks guys. Yup, threaded. All done.

I’ll make it simple and shut the main, open one lowest and maybe one highest fixture, have at the repair, and expect some water.

If occupants are present, to avoid unexpected release of vacuum, I’ll ask them to open all of the fixtures plus flush the toilets.

If you are soldering it ,an old trick I use for
dripers is to use white bread packed into the pipe,soaks up drip.

All of these are good advice.
If possible, open a faucet that's above where you're working (to let in air) and open another below where you're working to drain any residual water that's still in the pipes. You only need to drain enough to have the water level drop below the area where you're working.
There isn't going to be a huge amount of water if you can't drain it, but it's nice to stay as dry as possible.