Jeez, Mike, I'm really sorry that you had such an experience with the locals. Maybe, with luck, you can be a force of change so that others following in your footsteps will have a better experience. More on that later.
1. Most projects never get finished (9 in 10). Likely any project I take up will never get finished.
It's true that a lot of projects languish due to insufficient funds, interest, etc. That said, there are thousands of flying homebuilts, many of them RVs. Some people finish their projects quickly; I've been at mine since 1994 and I'll be finishing in a couple of months. Only you can gauge your level of commitment but determined people finish their projects all the time. Be one of them.
2. Even if I do finish, there may be no engine to put into my plane because Lycoming quit making them. (huh?)
WTF? I never heard this and I'm sure it would be a surprise to Lycoming, too. Not only that, but there are clones (my RV-6A will have a Superior IO-360 that I built myself at their facility) and alternative engines available.
3. Even if you find an engine, airports are disappearing off the map purchased up by developers. There's legitimate, current, ongoing threats to this EAA chapter's field. I may have no place to fly.
You'll have a place to fly. Some airports do close. Hangar space can be difficult to find and afford. I was told that most people locally go to airports up to an hour away and often do their final assembly and initial testing several hours away near Phoenix. When I went to the local airport, it took me two months on the list to get my hangar. At about that time, the airport got a new manager who's been very favorable to GA, largely due to the efforts of local pilots. And the local EAA chapter has not been very big; fortunately the EAA is not the only force in GA. We're trying to improve, though.
4. My rivets will likely never be airworthy.
Ok, I'm coming back to the "force for change" thing. I learned to rivet on my tail kit. At that time, there was no Alexander's or practice kits or the like. An A&P IA from the cargo airline I worked at came to my place and taught me to shoot rivets. Naturally I dinged a few but he said they'd be alright. I proceeded, pretty much on my own. Eventually, I got the airframe into a hangar (this was after a couple of moves) and decided it was time to get a tech counselor to look at it. The local guy is something of an institution (I found out later) and told me that my work would never pass. When pressed, he admitted it was safe, just not pretty enough for commercial work. After recovering from my initial shock, I got opinions from A&Ps I knew, other builders, even a DAR who was inspecting a friend's propjet. Essentially, I got an old fart with an axe to grind; everyone else thought the project was just fine. So my friend with the Lancair and I have decided to apply to be Tech Counselors so that other builders in the area won't have to go to this guy. By the way, my riveting has gotten much better, but I still have the occasional "oops".
5. I need to fly to Vans to inspect their facility and learn about construction.
It's a fun thing to do but "need" is rather strong. Order the info video and find some local builders to teach you about construction.
6. I need to fly to Oshkosh to see what's happening in homebuilts and stay there for the week taking classes.
Another fun thing to do, but again not necessary. A rather famous RVer had to build his RV before he was
able to get to OSH. I'm referring to Jon Johannson, the Australian who has flown his RV around the world a couple of times. By the way, when the nay-sayers get you down it wouldn't hurt to read his book. All along he was told "You can't ..." and "You'll never be able..." - not just about the RV but about his schooling and his career as a male nurse - and he just put his head down and did it anyway.
7. I have to fly to some class on the East Coast to learn how to build (or my rivets will stink).
Yes, the only good riveting classes are on the right coast. Seriously, what? Yes, those classes are helpful but there are other ways and places to learn to rivet.
8. The real cost of aviation limits access to the sport to all but the very rich - even if you don't go broke building the thing, you will maintaining, insuring (if you can even get insurance), hangaring, and fueling the thing.
Hmmm. This one's a hard one to answer. Not because it's right but there are nuances. First, show me a hobby that isn't expensive. I think I've been spending about as much per year on the RV that I used to spend on competition R/C sailplanes. At least I'll eventually get to ride in the RV. But aviation can be expensive. Again, only you can evaluate your (financial) commitment to the project. I can only tell you that I don't mind the dollars I spend on my RV; the rewards of building are worth it. And I haven't even flown it yet. And I'm already looking forward to my next one (an RV-10, I think). I was a $40k computer programmer with a wife in med school when I started; I planned on a simple IFR panel and a rebuilt engine. What slowed me down was a lack of building space until we got settled in Flagstaff; by that time the wife was a doc and I was able to change my plans to a new engine and glass panel. But I'm still pinching pennies; we've got a mortgage and student loans to pay (plus, I've gone back to school) - no way could I afford a commercially built new aircraft. All I can say is, if you desire to do a thing you will find a way to finance it.
9. I need to make all the decisions about avionics and engine today or I'll get lost in the project.
That's handy, but if your project takes a long time (like mine) then your situation may change. The best advice I wish I'd been given before it was too late is to plan for the most elaborate setup possible. If you plan for full night IFR, you will put in the wiring routes (conduit) and antenna locations, access for equipment mounts, etc. That doesn't mean you actually have to install all that. In fact, you could equip as simple VFR. Then later, you could change your mind and easily add/change equipment. That said, I had to do a lot of revision as my plans changed; it was only more difficult than if I had planned ahead. If you like building (I do) it's not a frustration; it's fun.
10. Ultimately, don't bother. If I really must do it, it was suggested, just buy a certified plane (no, I'm not kidding).
There are some people who are not into building. There is another RV builder on the field who partnered with another pilot to buy a flying RV-6A. The partner admires our projects but has no interest in building his own. When all is said and done, he will eventually buy out his partner and have the plane he wants without what is, to him, the hassle of building. Meanwhile, his partner has a plane to transition in while he completes his project. Both guys are happy and why should we question their choices? What route you pick is up to you. Personally, I'd enjoy the building as much as flying (good thing, too; I haven't had many hours since starting the project).
What all those points above boil down to is where your commitment lies. It's worth thinking about but if you already know the answer is that you want to build an airplane then don't be bothered. Relax, take confidence in your own decision, and build away!