First ever brew was AG (now some [ok a lot of] comments & Q's)

Why did I do AG on my first attempt? Well, because I'm a sucker for punishment. But really, I enjoy creating more than what's been created.
Q: I am curious how many other people went this route?

I brewed up Northern's Phat Tyre clone with Wyeast Belg. Abbey II (1762). Made a 2L starter.

I used half tap, half RO. My tap is >200 mg/L CaCO3 and >250 mg/L TDS, very low Fe and Mn, city doesn't report Mg. Cl- not chloramine, degassed the water 24 hours ahead.

Lesson 1: Do not try to step mash in a cooler (at least not the first time). I ended up doing a half baked decoction with a small % of the grain... twice, but didn't heat it to boiling temps.
Q: I did a protein rest at 122F because the grain bill was 50% Belg. Pilsner. Was that a stupid thing to do? Better to just target 152 in one shot?

Lesson 15: Get a cooler with a side drain, broken siphons are a PITA. Yup, I "fly" sparged too. Told you, glutton for pain. Result: the sparge was much too quick, and probably contributed to my OG being 1.047 (post-boil), which was on the low end. I know what to do better next time.

It fermented a bit dry at 1.008. I left it for 3 weeks total in the primary. No secondary, based on readings here.
Q: I was expecting a FG ~1.012 +/-. Too low mash temps over total time maybe? Might also explain some lack of body.

I tasted it today, and here is what I'm finding:
-The isopropyl-ish smell I was getting at week 1 is gone.
-Carbonation is a little low, but I will give this more time to develop.
-Head... What head? Almost no head. Mouthfeel is a little thin too.

-There is a slight metallic taste on the finish. I think what I'm tasting here though is the hop bitterness coming through more than it should due to the low FG. (1oz Perle @ 60, 1oz Hersbrucker @ 10). It's more of an astringent metallic bitterness. It's not unpleasant, it's just... there. I don't think it's an infection. I sanitized absolutely everything, StarSan. Everything I have is copper, glass or stainless.
I expected a little bitter, based on an OG vs IBU chart I saw around here.
Q: With those hops, and a young 1.008 beer, would you expect some kind of metallic aftertaste? Tannins from my whacko semi-decoction maybe?

I've never tasted the real Fat Tire. I wanted to taste mine before the real one. If I like mine, who cares, if I don't then I'll know how far I missed later.

So overall, I like mine. It turned out drinkable, very clear amber, a little thin, but should be nice for spring.
Q: What would you do next? Try the same batch, learning from the first cockups, or do something else?
The chemist in me says remove variables, the drinker in me says more beer more kinds.

Cheers & thanks for the hours (months) of research you all have provided.

I started out all-grain. Went pretty smoothly, all things considered, though it still was sort of like a crazy puppet show with no puppetmaster. I had a degree in biology, and a fair amount of training in chemistry, which helped immensely. I don't recommend starting AG to people without that sort of experience.

My first beer came out decently, though nothing like I planned and with some off-flavors. Water chemistry (a variable I wisely didn't let myself get into at that stage) probably killed me there. I have very hard tap water. Splitting tap with RO is a wise thing to do, and an easy option I wasn't aware of at that time.

About the protein rest: they can be useful, but are a kind of tinkering thing. I would just do a single rest around 150F (+ or - depending on style) for the first few, until you're familiar with the process and your setup. That may have contributed to your lack of head and body. It's hard to say if you didn't have tight control over the mash, though.

Get tight control over a single-infusion mash. Then expand your horizons. Don't fly sparge, the bump in efficiency isn't worth it unless you have a fancy setup for it. I get 85% + efficiency with batch sparging.

I don't know much about the metallic taste, as I've never run into that problem. I should probably say nothing here as a result, but let me throw this questionable advice out: I would suspect water chemistry before anything else.

If you want to remove variables, you could start with all distilled water and add salts until you get 'ideal' brew water for the style you're making. It may be instructive, at the least.

As for the last question: I would try something similar, in the same ballpark, but use a different recipe. I brewed only Belgian strong ales for my first four batches, just to figure out how things changed with different recipes. But I used a different recipe every time. It really expands your horizons without leaving you clueless, or jaded on a single recipe repeated over and over.

I'm glad you like your first beer, and welcome!

Cheers from the Skyforger