hey nic :)
bfing can be different for all babies, just like all pregnancies and births and babies are different, your body can react differently each time.
i was leaking from abouty 25 weeks with my first baby ans well, went on to bf for a fairly long time. so i would definitely say that leaking now is a good sign! as for expressing- do whats comfortable for you. if its only a small amount it should be fine, but remem,ber that prolonged continued nipple stimulation can bring on contractions so you should try to only do it for small amounts of time, but enough for you to relieve the pressue/discomfort or pain will probably be harmless. it wont *cause* premmie babies, unless you like sat there for an hour or more expressing iygwim. 5 mins or so at a time wont do you any harm.
as for milk coming in- well, we successfully bf with all the girls. but that said, it felt like it took a lot longer with dd3 for my milk to come in. i had her friday night, and my milk didnt come in til monday night- i went home tuesday with her. but it felt like it was sooner with zoe, i had zoe thursday arvo and my milk was in by saturday morning, and well with rhianna i was still bfing zoe at birth so my milk just changed to colostrum for about half a day then it was milk again by 24 hours after birth, and lots of it. i'd be looking at milk increasing foods you can have as often these things can actually help a lot more than medications can. maybe look at making lactation cookies before the birth and packing them in your hospital bag if you get a chance, or having them stored and getting DH to bring them in when you have bubba
brooklyn, was also my only baby to actually lose weight before we left hospital while being BF. she lost about 100grams i think it was, so i panicked, but even still those first few days of colostrum were good for her and eventually the constant feeding made the milk come in and continuing helped my supply keep up.
i think though with you having milk oproduction, you might have it a little better this time around. it can take up to a week for your milk to come in after birth, some babies do lose a little weight in this time but mostly they told me my baby wont starve and didnt need anything else (my baby was healthy though, had no bsl etc issues so for other things it might not be as ok) just to keep feeding as the colostrum would keep oming til the milk did. i really hope things go smoothly, i would check out and see if there are any LC's around as sometimes they are the people who do birthing classes, so you might be able to find if they will be around when you are due or at the hospital often so you can call on them for help if you need it.