One thing I would add, use at least the Medium strength PVC glue (normally comes in a BLACK can), not the all purpose (in a Red can). The black definitely holds better, but it does weld faster. Also, use the clear cleaner/primer, not the purple stuff (that can make for some really "pretty" installations).

For cutting very tight connections, you can buy a wire PVC saw, only about 5 bucks. It is very difficult to do real straight cuts with, but it can get in places that a normal saw won't. You can also buy fine toothed and/or masonary blades if you have a power mitre saw, these work very well. Clean the edges real well, sand paper works fine.

Clean, clean and clean again before using the glue!

I normally test all my connections (for length and fit, not for pressure) by coating the ends with the same silicone goop you use for fittings. This lets you try everything out before the final weld. BUT, you have to really clean the connections with the PVC cleaner before gluing.

On solar, if your panels don't include a bypass valve, you should plan on adding one. It makes fine tuning the flow through the panels much easier and also will allow you to do maintenance on the panels while the pool is running.