I'm a big fan of spaflex myself. I use it for my returns, it cuts down on vibration noise, and sometimes that little bit of flex is just what you need to get where you are going. Put ball valves on anything you might need to throttle back or shut off..............both sides of the pump, on your drains if you have more than one (so you can balance what goes where). Unions are great, put them on either side of your pump, makes it easy to take it out. Just be sure your unions are between the pump and the ball valves, that way you can make sure no water escapes while you are working. I have unions on my twin drain lines just below tank level, makes it easy to get the in-sump plumbing out if I need to work on it. I tend to stick unions on anything that I might want to take apart later.

There is nothing wrong with hard plumbing everything in, I have done that before too. Some of my tanks are "hybrid" using both spaflex and sch40 pvc at the same time. It all really depends on your application, how comfortable you are working with either product, and what you are looking for as an end result.

Use primer and glue on anything that is under pressure, or might be under pressure at any time in the future. Yes, you use both on the spaflex. I glue everything on both returns and drains, I don't like surprises, and I don't like leaks. Unglued joints can vibrate or work loose over time and start leaking (just because a drain line isn't supposed to be under any pressure does not mean that a rogue turbo snail won't stop it up and possibly cause a leak). Do not glue threaded fittings, and yes, use teflon tape. Don't use pipe dope, it could possibly leach into the water.

I can't offer an opinion on pumps, since I'm not familiar with either one. But IMHO Justin is right, use the lower flow for your return, to prolong fuge/skimmer time.