Checkvalves are great until they fail. And when they do, they do it spectacularly. I've never installed one in 8 years, and don't plan on ever using one. The ones Home Depot sells may have a metal spring in them, which can/will rust. MarineDepot sells the kind that are safe to use, but again I wouldn't bother.
You do want to drill an anti siphon hole 1/2" beneath the normal water level. So don't bother with that at the moment, because you don't know where the normal level is (precisely anyway). Once you've filled up the tank, you can see the spot. Then just add the holes, as I recommend two holes per return, to break the siphon. One hole works, but invariable that is the precise moment a snail has decided to park on that spot to get a nice pulsing massage, or the hole is clogged with algae.
Now that you have the holes, turn off the pump, let the tank drain and observe your sump. You should see less water in the sump this time, and more water in your tank.
The reason I was able to get my tank done in 14 days is because I decided I wanted it done and didn't let anything else get in the way. I know that one day out of the 14, I didn't do a thing with the tank probably because I had to work a bunch. But the other days, I was determined and set my mind to it to not stop until each goal was accomplished. Also, I know I had a couple of helpers coming over lending a hand at least 50% of that time, cleaning old parts or just holding something to be helpful. It was really a lot of fun, and I remember lots of pizza, snacks, drinks... and their girlfriends coming over.
I think my not having a wife or girlfriend helped keep me less distracted.
Years ago, I used to look at projects as overwhelming tasks, and dreaded how long it would take to do things. However, somehow over time a change occured, and I could suddenly estimate the duration of each project in minutes, and it was easier for me to get in there and deal with it. Knowing the installion of the sump under my 280g was going to take all day, the new one sat in the guest room for about a month. This was a project I couldn't do alone, because the sump was so large, and the old one was so heavy it took 4 people to put it in place. So I blocked out a day, had some guys stop by to help pull out the old glass sump, and I got under the tank and removed the existing plumbing to install the new. About 12 hours later, the new one was up and running.
Conda, you're making great progress and really don't have a lot to go. If you can't align things perfectly, use some spaflex in those particular spots.
Gluing it together will be quicker than you think. You might even practice with a scrap. Just in case:
Apply the cleaner liberally on the inside of the fitting, and then on the outside of the pipe. The fitting should have no white areas where the pipe slides in. The pipe should have no white areas and should have the final 1" thoroughly purple.
You do not need to wait for the purple to dry. Apply the glue to both pieces the exact same way. Press them together fully, then twist just a fraction (1/8" is fine). At this point, you may have some glue leaking out of the new joint. Take your finger and basically smear/trace the spot where the fitting touches the pipe to fill that grove all the way around (or as much as it will spread). This is just an added layer of glue, plus it makes the connection look cleaner. You could use a rag to do this, but I just plow on forward.
I always glue over something like newspaper to catch all the many drips. The purple doesn't wash off, so protect everything that you care about. The product won't hurt your hands, and after a couple of days your fingers will look normal again.
If you are assembling this in segments, you can sometimes look inside your fittings to see if excessive glue has puddled up in a spot that is reachable. This doesn't happen all the time, but if it does and you are so inclined to remove the excess with a rag or something, go for it. You don't want areas that can act as obstructions internally, so look for these when you can to make sure all is well.
Remember, the glue sets quickly. When you press it together, hold it for 20 seconds because the pipe will gently press back out of the fitting if you don't. Holding it keeps it where you want it.
And once glued, you almost never can get them apart. There are ways, but it is usually just simpler to leave it be, cut it off and put a new piece there using couplings. Couplings are cheap and work great.
Unions are a nice alternative if you think you'll need to remove sections of pipe. That may be handy in a few locations, but you better have a ballvalve above that union to keep the water in the tank.
