Welcome! It's terribly exciting getting revved up for that first build. I can FEEL your enthusiasm clear out here (in the middle of the Pacific ;-)
It took me about 4 months to scratch build my L1/L2 rocket. And I learned more than I thought possible. (only because I didn't think there was that much to learn - it's just another rocket, right?) Wrong. Dead wrong. In fact I built two identical ships, side-by-side knowing from all the youtube I watched that a CATO was possible. It took me 4 flights to complete Level 1 & 2. #1 fatally zippered. #2 Lvl1 success. #3 thought lost forever (there went $600 - bye-bye birdie!) #4 lvl 2 success. #3 was found 3 days later with a small zipper in the side. I was extremely thankful I made two rockets. I flew them both, and repaired them both.
It doesn't matter how careful you are, stuff way beyond your control happens. If you're not willing to toss the cash in the dumpster or the desert, then maybe back up a step or two and test on smaller less-expensive airframes.
Here's a couple of suggestions. On epoxy. I used 5-Min 2-part, RocketPoxy, FixIt epoxy, JB weld, Bond Aide (in the field repair), and PC epoxy. As well as wood glue and super glue. I will never use JB weld or PC epoxy again. They are so incredibly hard to sand. Just don't. Unless you love to sand. FixIt was the easiest to sand and works beautifully when thinned with pure alcohol. RocketPoxy is somewhere in the middle (in terms of sanding.) I found FixIt to adhere best to plastics (I don't mean fiberglass - I didn't need to glue to any fiberglass) - with proper surface prep, FixIt adhered best. RocketPoxy was the worst. I will admit that at first I didn't do a good job of prepping the plastic surfaces and RocketPoxy just fell off. Lesson learned. I never did discover a sure-thing for epoxying to aluminum. *sigh* - there's still more to learn. ;-)
RockSim. I use OR (Open Rocket) in the classroom and RockSim for all my design and simulation work. I've been a bit baffled when reading complaints that one has to pay for it. I'm thrilled to pay for such a solid piece of software that does what it claims it will do with such stability and accuracy. Absolutely no regrets. The folks who spent their time and knowledge to develop RS have well-earned my dollars and loyalty. OR is great in the (elementary STEM) classroom since it is free after all, and it does what the students need to do without much fuss. But, RS has a broader feature set.
Your dreams smashed? No Way! You're going to have more fun than is legal and no one can stop you
Pics of my Cert vehicle, the Rudy III. 38mm 4" BlueTube. The first test flight on a G.