I wouldn't buy a horse if you're planning a baby in the next couple of years. It's hard to appreciate beforehand just how much having a baby/ young child changes everything about your life, and just how hard it is to get out of the house with them!
Some small children would be happy to sit quietly and play whilst you see to the horse, but most wouldn't, especially once they're mobile (any time from 6 months old), as most won't just sit happily in a buggy, they want to be out and moving around, exploring their environment.
Also, you don't know how your body will cope with pregnancy. I was adamant before I became pregnant that I would continue to run regularly and exercise daily throughout pregnancy. My body had other ideas, and I couldn't manage more than a brisk walk from about 3 months in, despite being very fit beforehand. I would have really struggled with yard duties, and wouldn't have been able to ride, and that was a fairly uncomplicated pregnancy.
I would suggest getting a part-loan for now, so that you can get to know the area from a horsey perspective, find out about different yards, build yourself a network of horsey people. Also with a part loan, if you need to give it up once you're pregnant, or if things become too much once you've had the baby, you can just give notice, rather than have to worry about selling/ rehoming/ loaning the horse.
Once your youngest child is ready for regular nursery (from about age 3), if you're still keen, you could look at getting your own horse, as long as your DH is ready to step up and parent for much of the time at the weekend, and you can get cover for your working days. Remember also that as children get older they develop hobbies and interests of their own, which take up time and money outside of school. My son loves riding, but isn't bothered enough about general horse care to have a pony of his own, and wants to do other things too. I spend a chunk of my evenings and weekends taking him to his other sporting activities, which is part of parenting, but wouldn't leave much time for daily yard duties.
For me, even with a 10yr old DS and a part-time (but long hours like yours) job, I decided that it was better to part-loan, rather than spend lots of family money on a horse (therefore limiting DS's hobbies and family holidays), then have to pay livery, or find someone reliable to part-loan my horse to cover my working days and half of the weekend. That said, I'm more of a happy hacker than anything, so not bothered about competing.
My horse's owner has two young children, one primary aged and one pre-school. By the time I got involved, she hadn't ridden in two years, since becoming pregnant with second baby, so horse had been turned away, apart from a friend of hers riding occasionally. She's had DHorse for years and didn't want to sell her, but horse wasn't happy just being in the field. She's happy and thriving now being ridden three times a week, and the owner will be able to start riding again once her little one starts nursery this year.
Apparently it's very difficult to find a reliable and experienced part-loaner, so it should be fairly easy to find something, but this tends to happen best by word of mouth, if you have any contacts locally who could put the word out? I have seen competition horses part-loaned before, with the loaner and owner splitting the competing weekends between them, if that' more your thing.