I have a 19 month between DD1 and my twins. And we moved 300 miles when the twins were 3 weeks old, so I didn't really have a support network (other than my - lovely - inlaws). It wasn't easy at first, but we got through it. They are 15 and 14 now and it's (mostly!) great. I love that they're broadly at a similar stage at the same time - makes things like holidays, days out etc really good.
Tips: lower your standards where you can. We were able to get a cleaner, but the weeks she didn't come, I'd just do the absolute minimum I could live with.
Accept help that's offered.
I went out every day, because I always have and I felt the walls were closing in if I didn't. I had a double buggy and a sling, and DD1 quickly got good at walking alongside me (she was fully out of the buggy much earlier than any of my nieces/nephews, through sheer necessity). But if you find it easier to stay at home, don't beat yourself up with ideas that your babies are missing out by not going to playgroups etc - they're not!
One unexpected benefit was that, when I had DD1, I really felt like I had to be doing things well. I think it was probably largely internal pressure, but maybe some external too. When I had the three, I felt like I was winning just getting us all through the day and other people seemed to too!
Also, tiny practical tip - don't buy the babies clothes. Keep them in babygros - it's a lot simpler and no one cares what your babies are wearing. I put mine in clothes at around 4 months I think.
You'll be OK. It's been hard work sometimes, but it's also been the greatest thing. I wouldn't change it.