Hiya! Congratulations on the imminent arrival!!! I think technically if you're planning on expressing then it's not actually "combi" feeding, it's just breastfeeding with the occasional bottle which is precisely what I did, and what I plan to do with baby #2 (that I'm newly pg with!)
I'm not sure if you bf your first so apologies if this sounds like i'm teaching you how to suck eggs, but in order to establish your supply and to ensure your baby has a good latch, for at least the first few weeks I would try to exclusively breastfeed. Bottle feeding is a lot easier for baby as they don't have to work anywhere near as hard for the milk, so you don't want to encourage them to prefer the bottle and end up rejecting the boob. I do think it's great to get baby used to taking a bottle early on, so by all means, express within those first few weeks and give the baby a bottle here and there, but personally I wouldn't do 50/50 straight away for fear of boob rejection! My son was back in hospital at 2 days old with jaundice and they made me express and top him up with EBM, and he never actually rejected the boob, but when we left hospital after 5 days I only gave him a bottle 2/3 times a week to make sure he would always still take it, but never needed to do it more often than that.
One thing I would say - is that bottle feeding EBM is actually more laborious than you realise. Firstly, I hated pumping. It was tedious and dull and took forever. Secondly, I then had to freeze the milk, then when I needed it I had to take it out the freezer, defrost it, then heat it in a bottle warmer all before baby could drink it. Don't underestimate how convenient it is to just whip your boob out whenever baby starts crying. Get yourself a good breast pump (I liked the medela swing) and if you ever struggle expressing, try doing it while having skin to skin with your baby, it always helped me get that bit extra. Best of luck and enjoy your lovely new baby!