what pump should i look into

New to all this but currently trying to set up a Rainwater Harvesting system for whole house use (except drinking). Looking into strong enough pump that will push water thru the filters and end up at around 5 - 6 Gpm inside at maybe/hopefully 40 PSI. Will tie pump, UV and solenoids to solar.  

There are a number of factors you need to consider first.
Filters
- maybe run a series of larger to smaller filter medium so the filter does not block too quickly
- aim at large surface area filters to ease the effort required to push water through
- Consider disc filters which can be cleaned against cartridge filters which cannot.
Water flow
- check 5 to 6 gals per minute is what you need
- check 40 psi is needed.
Flow and pressure are linked.

A larger filter will make it esier to get a higher flow and pressure at the taps.

Each pump manufacture has charts which will show you the capacity of each pump and the operating pressure.
I am not sure if you will be able to get cahrts for filters that detail the pressure drop across the range of water volume through the filter, but look for them.

We have a flo-jet pump that we got on Amazon that we love. That thing pushes water like mad.