When to pump

Im currently in 3rd trimester, and want to prepare myself in the event that my milk kicks in very slow or if my milk supply is very low. For pumping wise, to stimulate more milk. If baby manage to latch - do i pump after every breastfeed session ? Is it instantly after or wait for few minutes ? If baby dont know how to latch and milk supply still very low - do i feed baby formula for the time being, but at the same time pump every 2-3 hours to stimulate milk? If the milk output from pumping session is very very little, do i put in a milk storage bag and leave it in the chiller or freezer ? Hope mummies can guide me on this #FTM #pleasehelp