Returning to work (EBF)

Can some of you breastfeeding ladies give me some advice and tips!?

I’m returning to work in 8 weeks I’ll be doing two 4 hour shifts and one 9 hour shift . My boyfriend will be looking after our son however he is EBF and doesn’t take a bottle (something we’re going to get him into having over the next 2 months) so we don’t know how much milk he actually drinks. My question is how much milk should I be leaving for a 4 hour shift and a 9 hour shift?

Also any tips on being at work and pumping etc

Thanks in advance!

P.s our son will be 8 months when I return and will be on 3 meals a day.