breastfeeding tips

I just had my daughter on Friday (9/16) and I get the chance to do skin to skin when I can (she's in the NICU) but I'm also pumping every two hours to try and increase my supply. So far I'm on day two and I know ifs still a bit early but how long would it take until milk comes in? Do I just keep supplementing with formula which I don't want to do until it comes in? breastfeeding is completely new to me