Trying to finally get my first Muscle Car - I’m nervous

You're not insane. I've been daily driving a classic mopar for over 12 years now. First my '72 Challenger and now my '74 Duster. I haven't even owned a car newer than I am in that time, the '74 Duster has been the newest car I've owned since '08.

Now, I do all of my own work and I grew up in an auto repair shop. And while a classic as a daily driver is possible, I wouldn't recommend it to someone without a decent mechanical background. I'm not saying don't buy one, I'm just saying don't sell your daily just yet.

As for the rest of your list
1. Good advice. Especially looking at old cars. Unlike new ones you can't just buy the next one over on the lot, so, there's some excitement in finding one you want. Which can blind you to the issues of that particular car. It helps to look at a bunch, you get a better idea of what to look for. On that note, don't be afraid to go look at other classic mopars, even if they're not "the one". If nothing else, you'll see some good/bad things to look for. And who knows, you may change your idea of "the one". My Challenger was the first mopar I looked at, and I blew it even with a long history in classic cars. I love it, don't get me wrong, and I put 70k+ miles on it. But the thing is a rust bucket, and I saw half a dozen cleaner cars for sale in the 3 months after I bought it. Patience would have saved me a small fortune in rust repair.
2. Terrible advice. All classics are money pits. Most of your money is made on the purchase, the rest is inflation and what's currently popular. The money you put into them after you buy them is almost always a loss. This is especially true if you're paying someone else to work on them. I love working on my cars and ALL of them are projects. Which is why I can say I would totally have been "ahead" in most cases buying a finished car. If you've got the money to buy a finished one, don't buy a project.
3. Definitely helps, especially if you can find someone you trust
4. Investors are assholes that have ruined the hobby, and most cars are money pits. Investment quality stuff loses value if you drive it anyway, so, that's not where you're at.
5. Yeah, probably, but life is short. If you don't enjoy it now, you might not get the chance to later. No guarantees.
6. Maybe. But if you decide it's not for you then you sell it. If it's only a few months, you shouldn't lose much money and then you'll know
7. One is never enough.
8. They're not easy, but if they were everyone would have one. And if it's too big of a pain, sell it. New cars break down too.