It really does depend on you and how comfortable you feel. I feel that you should be knowledgeable about the care and upkeeping of a horse before you own one or you will be in for a big suprise! haha Do it when you are ready to have a friend for a long time!
Honestly it's super subjective. If you have enough money to look after a horse properly it's fine to get one at any level of riding however it's easier when you've been riding for awhile. If you've just started and your looking for a horse I would defiantly suggest leasing. For me the best "first horse" would be something that's been there done that. This can really help you work on your riding and not have to worry about training the horse!
I got a pony before I started riding. I'd probably sat on a few but never had a lesson. She wasn't a suitable pony either, but after a few years we eventually worked it out and did pretty well. So, as the others stated it really depends on what your situation and level and future even are. Not saying mine was a good way!
In regards to what is a good first horse, as a general rule, one that you can learn on, something with a nice nature, has been out and about and ideally has had other beginners on it.
It honestly depends on the rider, i got my first horse after years of riding because of financial things, but others get a horse within the first year. The main thing is ensuring that you can properly care for the animal😊 in my mind there is no “ideal first horse” every horse fits and loves a different rider😊