Hi, Dart! Welcome to the forum and back to the sport!
Some tips from a fellow big guy:
Avoid problems:
A sexy frame that has mechanical issues sucks and you'll curse it when it fails on you when you are going hardest (usually in a race). Failures include slipping track ends, seatposts dropping into the frame several millimeters, seatposts tilting, not being able to align the rear wheel easily (frame note aligned properly), etc... Issues like these usually occur to many people, so asking around will help.
Fit over materials:
You'll undoubtedly be faster on a properly fitting steel bike than an ill-fitting carbon super bike.
All carbon isn't the same:
The density of the weave of the carbon can be different. The layup (how the carbon sheets were positioned before hardening) can be different. Both of which affect the properties of the bike. Not to mention quality control (or lack thereof) of the company making the product. Again, reviews and feedback will help here.
Fixies vs Track Bikes:
There are a lot of street fixies out there that may or may not be good for racing. The geometry for ideal street use is somewhat different than what's ideal for track use. YES, the stuff will work just fine. But, if you are spending money, you will probably want to know the difference.
Materials:
A builder can make flexy or strong frames out of steel, aluminum, or carbon. It comes down to the individual manufacturer and model. Reviews are vital in this regard. Aluminum is generally the happy medium in terms of price, availability, weight, features, and overall value.
There is a lot of hype out there. There are cheap frames that are crap. There are expensive frames that are crap. There are cheap frames that are awesome. There are expensive frames that are awesome. I imagine that you know this because you started the thread.
Bike frames are a journey. Very few people that stay in the sport buy 1 frame and never upgrade (or side-grade). Usually people will have a frame for a period then figure out what they like and don't like then look for a new frame that has what they like and not what they don't. The start of the season is like the first day of school. Everyone is checking out everyone else's new stuff.
A common mistake is for new (or returning) riders to buy a frame that is too small for them because it's comfortable. This is part of the journey. It doesn't happen all of the time, but it happens. I started on a 57cm frame and now I own 60 and 61cm frames.
There is a good bit of info in this thread:
https://www.bikeforums.net/track-cyc...ete-bikes.html Track bike offerings don't change much, so the thread is still somewhat relevant.
Also, if you want to see what people are using on the track, look here:
https://www.bikeforums.net/track-cyc...es-2014-a.html Generally, that thread is reserved for bikes that are actually used on the track, not street fixies.
Maybe ask questions in this thread to help with your equipment choices:
https://www.bikeforums.net/track-cyc...ions-here.html There are no dumb questions. We were all new once and the best practices continue to evolve.
As far as what you should get, it really depends on your budget and what's available to you. I think when you narrow your choices down to particular make/models, you'll get solid, actionable feedback.