Can I substitute a 9 inch tart pan with a removable bottom with a 9 inch spring form pan? Or even just cook in a pie dish? Don't want to buy

Most of the time, yes. You'll lose quite a bit on aesthetics, because the tart pan has the fluted edges and can hold the form through these flutes. It can also be a bit more difficult to work with (e.g. only having the crust going halfway up the sides of the springform pan, or not being able to easily remove the tart from a pie pan). But you can make it happen if you want to.

It completely depends on what you are making. A tart pan is much more shallow than a springform.

It depends on the recipe. A tart pan or a spring form will allow you to remove the tart/pie and serve out of the baking dish. If you make it in a pie dish it might be more difficult to remove. Also a tart pan is typically shorter than a pie dish. The crust for a tart pan may not reach completely up the side of the pie dish,