I know lots of people do have their children close together but I think the strain on your back and your core of being pregnant plus carrying around a toddler shouldn’t be underestimated. I remember seeing my 7m pregnant friend having to manhandle her 18m in and out highchair, onto mat for a nappy change etc and made a mental note to have a bigger gap than that!
12 hours a night at 7 weeks - I’m not surprised you feel great! But really you won’t know how your baby sleeps until you’ve been through the 3/4m sleep regression. It’s a biggie for most babies.
Are you breastfeeding? Breastfeeding through pregnancy can be a struggle (I tried it, milk dried up) and babies still need breast milk (or formula) until a year old.
Also what about the financial and practical aspect. Do you want a double buggy, two sets of rear facing car seats (is your car big enough?) two high chairs at your table, etc etc? Babies/toddlers need a fair amount of Stuff, do you want to buy it all twice?
I initially wanted a small gap between mine, but then I realised how much of a pain in the arse it would be in practical terms.
I’ve had a 2.5-3year gap between my three, it’s worked well. Not needed a double buggy, just the pram with a buggy board. Older ones can come out of the smaller car seat ready for baby. Only one child in high chair at a time. By the time the baby is 6m and throwing food the older ones have table manners and can help with teaching baby rather than joining in the ruckus. You can get out the Playdoh and supervise while you feed baby rather than being needed to help with play and ideas. Etc etc.
My friend was seriously ill having her second baby. She was in hospital six weeks. Her 3 year old could be left with the childminder full time (who was lovely and helped them loads, bless her) while her husband had to go back to work after his two weeks paternity. It’s worth thinking through what your options would be in that kind of scenario.