How easy depends on what you are wanting to do.
If you just want to put a cpu block in there with a 240 rad, pump and some soft tubing it is fairly easy and quite similar to using an aio in some respects. Hardest part is often getting all the air bubbles out.
Things get more complicated when you want to cool the cpu and gpu with multiple rads as you have to think about routing in the case more carefully. Where to put a fill port and drain port etc.
Then you can make it a little more complicated by using hard tubing. A little skill is needed for bending and cutting the pipes to the right shape and lengths.
As for cleaning, they’re not as bad as some people make out. I change my fluid once a year. Flush the system with some deionised water and then put the new fluid in. There is one note to say with that. If you use the pastel colours or other “thicker” fluids. They sometimes can clog the system and that does require some serious cleaning.