Yes, you can use a CSCR (cap start, cap run) on your pump, even if it's a higher HP than your pump. You can go up, just not down.
It won't save you much electricity, but it will use slightly less than an IR (induction run) box alone. The CSCR engages the start windings with the run windings, whereas a IR box only uses the start windings to start and then swaps to the run windings.
No comment on the booster pump. I suspect it will not work for what you want it for. It boosts pressure, what you need is more volume, not pressure. Enter the CSV vs. VFD black hole.