PVC plumbing is pretty easy. There are some good youtube videos around.
The mistakes I've fixed usually arose because of not thinking about the last connection needed, and being able to rotate the last glue joint, or a joint being slightly out of alignment, or a fitting that jettisons.
To avoid this, dry fit the pipes and fittings after you've worked out all the lengths, and just think through how you'll take advantage of the pump and SWCG unions, which can be left unconnected, allowing you to rotate an assembly of pipe and fittings into position. When dry fitting, pipe usually won't go all the way in to fittings, and with glue they'll slide in deeper. Take a look at it all while dry fitted, and imagine most fittings slid together a bit tighter. It will look best to you in future when it ends up plumb, square and level (possibly with some 45s if that helps with fitment).
If you blow it, and have to jam a last fitting in at a slight angle, back off and re-do whatever is wrong. When they slide in at an angle, the glue gets pushed out of the way and leads to leaks or weakness.
Most fittings slide in with no worries, you do a quarter turn as they go in, they grab almost instantly and all is well. Occasionally, a female piece will be forced back out slowly before the solvent grabs (not sure of right word, but I call it jettisoned) just after you've fitted it. Often it will still grab fine, if for example it's only jettisoned 1/8" or 1/4". To prevent, just be sure you can maintain pressure on the piece being pushed in for 15 to 30 seconds, and then watch it for another 10 or 15 seconds after to see if it's staying put. This happens more often on 2" than 1.5".
On cost, most of the stuff is cheap as chips. The exception is the unions that come with the pump and SWCG. So take your time and do those late in your gluing, so you can fix anything that didn't work out with a plain slip coupling rather than needing to drive to the pool store.
On timing, you have to work reasonably quickly after applying glue. Coating the female part first buys you a few extra seconds.
Otherwise, cut close to square (needn't be perfect, but close is best), sand off burrs (coarse wet'n'dry sandpaper works well), use primer, and coat both male and female completely but sparingly with glue (also called solvent). And always set the glue bottle where you can't knock it over, haha.
The glue seems to fly everywhere, and drip when least expected, especially little strings of it, and can be hard to clean off depending what it lands on, so an old towel to protect surfaces can be a handy part of the tools needed. I've never managed to get it off brick or stone. Wipe important drips away right away, or use acetone or rubbing alcohol while it's still soft. Once it hardens, you'll probably end up just living with it. If you drip it on just the pipe and fittings, it won't hurt anything and pretty much just looks normal, but drips on components might bother you in future. Good chance you'll paint the pipe anyway.
And anyone who tells you - you don't need primer, you only need to coat one or the other with glue, doesn't matter if the cuts are cleaned off, etc. - will get away with it 99% of the time because PVC fitment is very forgiving. One warning about primer though is not to dry fit shortly after you put primer on, the pieces can grab and be a pain to separate.
