Thinking from a pure tonal perspective, what's better, a low end bass with a high-end amp or a high end bass with a low end amp.
What are your thoughts?
It's almost hard to buy a really bad bass now. You just need to get something that works and has decent sound. Something on the level of the Squier by Fender series will give you good sound and playability without spending much.
I bought a piece of junk Japaneses bass when I started playing in 1965 (long before Japanese basses became good). Sold it in 1966 and bought a used 1965 Fender Jazz (YES!!). That was stolen in 1976 and I replaced it with my "White Lady" ('82 Jazz with maple neck and same neck profile that my '65 had) in 1985. It's a great sounding bass. But there's more to a bass than how it sounds. How it plays and how it feels to play it can be night and day different between basses. You reach a point of diminishing returns rather quickly once you start going over ~$500 or so. You can pay a lot more for a little bit better bass.
So get a decent amp first and then get a different bass if you want one later. One bit of advice on buying amps and basses though. Research the crap out of them and try them out if you can. On amps especially though, buy the best you can "almost" afford and always buy something capable of more than you need right now. That way you won't have to upgrade again anytime soon.
Why buy the best you can "almost" afford? Because it only hurts once to buy when you first make the purchase. Every time you use it afterwards you will be so glad that you bought it. If you don't go that route, you may very well find that it felt good to spend less money when you made the purchase, but you end up regretting that decision every time you use it - and that's an abysmal spot to be in.
So get a decent bass to begin with and then get the best amp and cab you can almost afford. I'd suggest you get amp and cab instead of combo just because it's easier to upgrade. Usually with a combo, you only get half the watts out of it as-is, but you have to add another 8 ohm cab to the rig get everything out of the amp. Not a bad thing until you need to get a better amp. Then you end up not only retiring the old amp but one of your two cabs.
Another combo approach is like the newer Eden E-series combos (EC). They are 4 ohm minimum amps WITH 4 ohm speakers included so you can get everything out of the amp that the amp has to give just with that combo. That's great at first, but expansion is difficult with this approach because the amp is already operating at its highest level. So to get around the chance of going below a 4 ohm load, it unhooks the internal speaker when you use the "external speaker" output so you don't accidentally run a 2.67 or a 2 ohm load on the amp and melt it. So now you have two speakers and only one is working. It's really only worth doing if the external speaker is a 410.
If I were forced to use a combo, I'd go for one like the Fender Rumble series that is OK to start with and you can add a second cab for larger venues for more power. This is especially true if you start with their 500-watt amp, which uses 350-watts by itself and ups that to 500-watts with an 8 ohm extension speaker. You can't do this very well with their Rumble 300 or lower. Even though the Eden combos are better sounding (IMHO), those who use the Fender scheme make more sense to me.
Again, the separate head and cabs will be more expensive to start with, but it makes upgrading as your gigging position changes much more versatile AND less expensive than it otherwise might be. And you never end up with an amp with built-in speaker that you can no longer use.