Does it require expensive machinery and/or a lot of space? I've considered doing it in the past for mine and my friends vehicles but never seriously investigated it.
To do it manually you need a bead breaker, a manual tire changing tool, and a manual wheel balancer, plus some basic tools. The tire changing tool uses a lot of leverage, so you'll need to fix it to concrete or similar. They're not expensive tools, but it mounts up, and you're never going to be up to the speed of the pros. Balancing is not going to be as good as the machines in the tire shops, either.
Note also that once you have the tire back on the new rim, you need a bead blaster to set the tire to the rim before final inflation - that's another tool, which also needs a decent sized air-compressor in order to work.
It's a large investment in time and money - research it well before moving forward.
Depends on the vehicles, sizes/profiles of tyres etc. Once a wheel is secured some tyres can be changed relatively easily with just levers etc. However most would be a struggle and others near impossible.
Pneumatic car tyre replacement machinery doesn't really take up much room, but it is expensive. With a little training though tyres can be replaced on these machines within minutes.
Tyres/wheels must also be balanced after any work is done regarding tyre replacement.