Congratulations that is lovely news.
DS1 is 19 months and DS2 is 11 weeks old.
Everybody was saying it would be hard but I think it's fine. Yes you have the odd hard day but you just have to roll with it because the next day will be better.
I find it easier and more relaxed with DS2 because he just fits into the routine of DS1. With DS1 you change your lifestyle completely but DS2 just has to fit into to your family.
Hopefully your first child is still napping in the afternoon - he is probably phasing out of naps! But if he isn't the best tip I can give you is do you morning routine then take your first child out to tire him out, let him run around and get exhausted, have his snacks outdoors and even lunch and desert if you can pack it with you. So when you come home all you have to do is give him his milk (if that's what you want to do) and he will go to sleep, giving you an hour or couple of hours respite.
You have to keep DS1 busy and he will be fine. Your second child just put the baby in a sling or wrap which will keep your hands free for your DS.
DS1 went nursery 3 days a week when I went back to work for 4 months. Then I dropped it down to 2 days a month before I went on maternity leave. I have now dropped his nursery to one day a week and he goes to his gran one morning and his nan picks him up in the afternoon.
Hopefully your family will help you with DS1 which will be a big help.
Main thing is to be organised and top of everything and stay calm - that way you will be fine with two little ones.
I keep on top of General housework by doing 30 minutes each day - concentrating on certain areas of house each day. And I will have one organising task each day which does not overwhelm me and I can concentrate on kids.
You will be fine you have raised one child the second will be a breeze
Good luck