North Texas freeze / potential upgrades

Like many others, we're having a few issues after the freeze in Texas. I decided before hand to do a quick semi-winterization of my pool equipment instead of leaving it running, as I didn't want to put extra strain on the grid or have any freezes during a possible blackout. Freeze mostly ended on Friday, I waited until Sunday to restart everything. I ran some cool water through the system via a bucket to handle any last ice and let that sit, ensured all my valves were free, then started it up. My pressure gauge died but no big issue to replace there. My booster pump (Pentair LA01-N) also developed a small leak around the inlet/outlet, I'm assuming due to the thread sealant cracking some. The motor developed a bit of a noise, but nothing crazy.

However, after running the main pump (Pentair Challenger CHII N1 1-1/2A / 346206) for 24 hours, it has developed a decent leak around the volute seal. I pulled it apart, ensured the gasket was undamaged (seems to be, but it doesn't seem to sit right in one quadrant of the housing) and put it pack together, getting the metal bracket as tight as I could without wrenching down on it, but the leak persists. I've ordered a new square gasket to try, and I'm planning on lubing up the existing one to get the leak manageable enough to at least keep the water moving for now. I figured I'd get a 3/4" PVC plug and just cut out the booster for now until I've got that fixed up as well. I've also noticed a crack in my inlet valve (Jandy 3-Way Valve) that isn't leaking, but is concerning, and I have had a few existing pinhole leaks that I've been too lazy to address and some other piping pieces / unnecessary elbows left over that I'd like to remove, so I figured I'd just re-plumb everything around the equipment and start fresh. Given that I'm already doing all of this, that the pump is nearing 10 years old and is a single-stage pump, and the booster is 6+ years old, I'm considering replacing the main pump with a two-speed or variable-speed pump, and potentially getting rid of the booster in favor of a robotic cleaner.

My current setup is as follows (~21k gallon pool, ~16'x32', 3' shallow end, 8' deep end):

• 2 x 1.5" PVC pipes from the skimmers join into a 2" PVC pipe, enter the 3-way inlet
• 1.5" PVC pipe from bottom drain enters the other side of the 3-way inlet
• 2" PVC out of the 3-way inlet into Pentair Challenger 346206 1.5 HP
• 2" PVC out of the main pump, immediately bushed down to 1.5" PVC
• 1.5" PVC into Hayward SP0714T valve head / Hawyard S244T sand filter
• 1.5" PVC out of valve head to salt chlorinator, to pool return
• 3/4" PVC tee pre-chlorinator to Pentair LA01-N booster, to pressure cleaner

My "optimal" plan in my head would be

• Replace 3-way valve, pipe 1.5" PVC out into 1.5" PVC main pump
• Replace pump pipe out (2" PVC -> 1.5" PVC) entirely with 1.5", with less elbows / left over pieces
• Cap 3/4" PVC tee, remove booster, replace with robotic cleaner

My main question here is, since I have a 2" inlet in the system, is there an issue with getting a main pump that has 1.5" inlet/outlet to match the rest of the system, or does it need a 2" inlet/outlet to ensure it can pull an adequate amount of water without burning itself out / ensuring enough water is pulled from both skimmers / bottom drain? And I'm assuming that because my piping is mostly 1.5", I'll be limited to 40-45 GPM? At that point, is a two-speed/variable-speed even worth the increased cost, or will it be mostly wasted? I usually run my pump 8 hours a day; I know the benefit of a two-speed / variable-speed is being able to run it for a longer time at lower speeds, but I'm not sure if there's a minimum flow rate that a pump can effectively run, or something like that, or if there's any major benefit at this pipe size to reducing the flow. My electric rates are low so I doubt I'd see much power savings, but more interested in reduced potential pipe maintenance. I've seen the Whipserflo 1/2 HP thrown around a few times as a recommendation instead for this 1.5" pipes.

For plumbing, the 2" pipe in/out of my pump currently is sch 80, then converts to sch 40. Any issues with just using sch 40, especially assuming less heat/strain with a likely smaller pump? And as far as thread sealant, the last time I used some (to replace my filter head) I used Rectorseal T+2 since I needed it in a pinch. Is that decent enough, or is something else recommended?

Outside of that, any recommendation on pump size/power/models, or on robotic cleaners?