Lucy Ruddle is a good one to follow on social media - she has just released a book called Breastfeeding Myths which is entertaining and good at separating myths from reality! Amy Brown also has a good book called The Positive Breastfeeding Book which has loads of info.
My best tip is to suss out your local support groups and go there starting from the end of pregnancy. Also, surround your social media with BF positivity and experts. NCT sometimes offer breastfeeding prep courses (or breastfeeding prep as an add on to antenatal classes) - well worth doing even if just to meet other mums just starting out. We have lost our breastfeeding "folk knowledge" collectively, so while generations ago you would have got info and support from your mother, sisters, aunts, friends etc, nowadays families are smaller and not every woman has children as soon as they are married, but also even the ones who do have children might not have breastfed, or likely had negative experiences. So to get that collective understanding and experience, you now have to go to someone who has trained in and is experienced supporting breastfeeding mums.
To answer some questions - leaking is quite individual, I never really leak except in the really early days a bit from one boob while feeding from the other, some people leak all the time. Most people find the leaking settles down when supply regulates around 3-4 months (6-9 months if you have oversupply).
You'll get conflicting info about pain, some say it's not normal, others say it is, I think in order to err on the side of caution, if you're getting pain ask and see if anything can be tweaked. I did find it a little bit painful at first with my first baby. The other two not at all. Some types of pain will get better by themselves whereas some are indicative of problems. Best to get an expert opinion if you can.
If you and partner don't smoke (or if partner does, consider kicking him out of bed!) I highly recommend looking up safe co-sleeping guidelines. You don't have to plan to co-sleep all the time, but breastfeeding makes you sleepy and it's beneficial to feed often in the early weeks so if you feel like you're going to fall asleep, it's safer to set up your bed just in case than to try and stay awake and accidentally fall asleep in an unsafe way/place.