Very cool name. Wish I had thought of that.
I am assuming you are referring to the Coolster when looking for performance but the following should apply to all 150's.
For more power, based on your description, first thing I would do is go with an air filter. In our track attack vids, there was a marked difference in performance with the UNI. Since your riding styles are mixed, I'd say you could benefit from the clutch mods. Since you do a good mix, I'd actually suggest 13 gram sliders and the yellow rear main spring. I did that once before and was pretty happy with that combo. Going with the 12 gram sliders I was not as happy an on my flat track there were not real gains.
For jetting, it can go many different ways. What I have learned is that different buggies respond in different ways. On these Helix machines, right off the bat with no mods, they like at least a 128 main jet. That doesnt' mean that yours would like that. No one can tell you specifically what jet to get until we know what jet is in it now, and how it responds to jetting. A helix you can move 5 jet sizes and still be within reason on the AFR to where it is not bogging or sputtering. On other machines, I have moved 5 sizes and the machine hated it. The problem is the carbs don't all come from the same manufacturer. Jetting is DEFINATELY a trial and error thing. I own at least one jet in every size from a 128 to a 152 skipping every other one.
As to which vendor, here's how I do it:
Which one is closest to me (thus can get me the product in my hands first)
Which one has it in stock (again thus can get it to me first)
Price.
you'll be fine with either one. Figure out what matters to you.
One thing I will say regarding your entire post is that you MAY find that you wish you had bought a 250. In most cases, the power difference in a 250 is considerable. Check out this vid here where I raced one of my 150's against a 250. (mind you I have driven other 250's that my helix would spank kinroad for example):