Hi hayley1
I've had DD since writing in here and have a 15.5 month age gap between my two. The best pieces of advice I can give are:
If somone offers help - take it!! I don't have any of my family in NZ so it was friends and my IL's that were offering to help me out (especially when DH had to go away for work for a week when DD was 6 weeks old) I didn't want people to think I couldn't cope so I politely declined and while I got through, it would have been much easier had DS gone to hang out with his Nana a day or two a week or I had said yes when friends offered to come help me out from 5-7pm for dinner and bath time.
Be organised - this is huge for me. When DS was in bed and DD had her last feed for the night I would get everything organised and laid out for the next day from a packed lunch for DS (yes, even though we were at home) to lunch for me, clothes for everyone and I'd usually get a head start on dinner or at least lay the things out that I knew I'd need for dinner. And during their day naps, I'd get their pj's sorted for that night. It sounds a bit OTT but I never once complained that I was too organised.
Keeping your toddlers routine - we still ate dinner at the table at 5pm (I would usually have to feed DD at the table) we still had baths at 6.15pm, still had his mid-morning nap - essentially, DD worked around DS's routine as much as possible and not the other way around.
Freeze Meals or ask friends to make meals instead of giving a gift - not only do you not have to cook, but you don't have to do dishes when all you want to do is go to bed!
Sleep deprivation, well I always seemed to get them down together at some stage throughout the day which was great as I could sleep too. But if your toddler can spend a day or morning/afternoon once or twice a week with a family member or friend you can sleep when baby does.
Also, DH and I took a child each for those first few months. DH usually got up to DS in the mornings and I would get up for DD (BF'ing meant this was the best way to work it). Also on the weekends DH would take DS out on boy outings so I could spend time with DD and of course - Sleep!!
All the very best, it seems daunting but it all just seems to work out