Hello AustinGuy,
Welcome to TFP!
I can't comment much on the pipe diameter. But the larger the pipe, the less head, which can also be achieved with multiple runs using pipe of a smaller diameter. It just depends on your setup.
Pentair, vs. Jandy. They're all good, it just boils down to preference, deals, warranty, replacement parts availability, etc... I don't have any 1st hand experience with either, just from the chatter here on the forum.
What I do know a fair amount on and can definitely comment with educated certainty, is the pump type.
Yes, your PB is rather wise and it seems not so much after your pocketbook. VS pumps are a waste of money and are generally not recommended unless your electric rates are over 20c/KwH. Otherwise you'll never recoup the cost of the expensive pump. Even then, there are many exceptions.
However, it seems the advise of your pb isn't as wise as it would 1st seem. As single speed pumps are an extremely un-cost effective choice.
The sweet spot is right at where the 2-speed pump lives. You run it on full speed for water features, suction side cleaners/in-floor and solar. As well as backwashing your filter if that applies and when youbwant increased circulation, say after a big pool party or dust storm, or such things. Otherwise, the rest of the time, for daily filtration needs, you run it @ 1/2 speed. Which moves 1/2 the water, yes, but... consumes only 1/4 of the electricity as full speed.
So even if you run it for 8hrs instead of 4,.you still only consume 1/2 the electricity.
See how awesome that is?
Lastly, the, next and possibly equally most important thing with a pump for efficiency sake, is this. Buy the smallest HP and amperage pump you can for your needs! I repeat, you don't need a 2hp whopping pump just because the pb says so. Of course, unless there's a reaaallllyy good reason for it. Best to ask here 1st if in doubt.
I suggest visiting the "pumping station" topic and reading the sticky thread titled: "Hydraulics 101: Have you lost your head".
The article contains much information on head loss for a given pipe diameter, pump speeds, pump efficiency, filter sizing (double the sizes for all but sand) and so much more.
Do read up in Pool School, link in my sig, while your pool is being built and also take a look at our recommended test kits. Link in my sig titled: "TF100 test kit".
You'll need one of these kits, as well as the knowledge in PS for the proper care and feeding of your new pool.
Lastly, please fill in your sig as instructed in pool school, 1st link, also your location in your profile under user control panel.
Thanks!
Tony.