First, welcome to XTERRA! I think you’ve got really good advice from the first replies and I’d echo them.
Socks: I don’t usually wear socks, but I don’t wear them in road tris shorter than HIM anyway. That said, I have occasionally had blisters, worst in muddy and sandy conditions (like Maui, etc…). YMMV.
Fluids: I’m a decent MTB rider, but I still typically opt for a small Camelbak, usually the 1.5 liter size. I just find it’s so much easier to sip out of frequently and even in semi-technical sections. Also, on the “easy” sections where you might want to drink out of a bottle, I find that I’m often surging to pass the slow folks who swim faster but aren’t very technically proficient riders, so drinking from a bottle isn’t a good choice for me there.
Pacing: As you’ve discovered, your power will surge all over the place with technical spots, maneuvers, little climbs, and passing people on double track. Compared to road tris, you’re be anaerobic and burning matches much more frequently. Just a reality with the explosive efforts that are sometimes required. Budget your energy and ride a bit more conservatively than you might normally do on the road, especially for the first race. Then you’ll have a lot more basis on which to judge for the next time around.
Gloves: if crashing is a real possibility for you, it’s probably worth putting on a pair of gloves, unless you don’t really care about coming in to work on Monday with scratches and abrasions on your hands…
The other big challenge about XTERRA is that if you’re not a FOP swimmer but are a decent biker, you will inevitably be stuck behind a crowd of folks when the single track sections start. This can be frustrating, and it is quite helpful to be aware of any passing sections in the course, and plan for them, ready to surge the moment you get the chance. Also, if there are any technical spots, be prepared that half of the riders in the race won’t be able to clear them, and will often be off their bikes and frequently standing right on the good riding line. Just a reality to accept and anticipate.
In the end, though, the XTERRA vibe is pretty chill and relaxed, and there is much less yelling at one another compared to some other types of events. Mostly everybody helps one another out there, and it tends to be a LOT of fun.
My $0.02.