Given the constraints (one body only - then one, two, or more lenses) I voted two. The reason is that's what I did with the two main systems I actually shoot most with. They are my Canon EOS DSLR system and my Hexar RF Leica M-mount system. Or, at least, that's what I did initially.
For the EOS DSLR system I bought camera, kit ("do most things adequately") lens and the best lens of the type I really wanted, which was an IS-equipped telephoto lens for wildlife shooting. I spent a bunch of money on what was my target lens (the tele) and the least I could on the "everything else" lens. The tele did everything I wanted, while the kit lens was "good enough". Sure, I've moved on from there. The tele has been replaced by something more expensive, yet better in every other way (except size and weight). But I got the photos I wanted and otherwise couldn't get with that lens, and it still does good work for my father. The kit lens has been retired as the paperweight it no-doubt deserved to be all along - but it hung around long enough for me to learn what was important to me in what I then regarded as "secondary" applications.
I did something similar with RF cameras. I didn't even decide to buy an RF camera until I knew what lens I wanted for the application I wanted an RF for. That lens was a 75 'lux, which I still have and still love. However, part of the affordable price of the 'lux was its having to be sent off for a CLA. I covered that gap by buying an RF camera kit - the Hexar RF and 50mm/f2 M-Hexanon lens (the boxed set). Using the camera and lens combo taught me how to use an RF in the way I wanted, so I was prepared for the 75 when it arrived. And unlike the SLR kit lens, that M-Hex is still one of my favourite lenses. (OK, I've bought way too much RF stuff since - but that's what got me started. And a 35 would have been a better "do everything else" lens for me than the 50 - but I didn't know that at the time. I'd always preferred a 50 on an SLR. Oh, and I'd have replaced that 75 'lux with something better - except for me there is[/u nothing better than that 75.)
I was in the fortunate position that having established myself with both systems I could then expand on them. But if "stuck" with both I'd be quite happy - able to meet my primary objective with each system, using the best (for me) lens I could afford for what I wanted to do, and having another lens to do, more or less, the "everything else" tasks.
...Mike