I'm the author of the answer on SuperUser that mook765 quoted. I'm therefore going to cut-and-paste part of that answer, and make some edits to it....
The EFI specification imposes no limit on the number of ESPs that may be present on a computer or on a hard disk; you could have dozens of them if you wanted to, and that would be fine from the EFI's perspective. Unfortunately, Microsoft is not so flexible; Windows officially supports just one ESP per disk (maybe per computer; I'm a bit foggy on that detail). I don't know about Windows 8 or later, but the Windows 7 installer will flake out if it sees more than one ESP on a disk; the installation will proceed part of the way and then fail. (At least, that's what it's done in my tests.) That said, if you create a second ESP after installing Windows, Windows will continue to boot and operate correctly, at least as far as I've seen. (I can't promise that it won't misbehave if you use some particular feature, though.)
Overall, then, in a multi-boot environment, I recommend restricting yourself to one ESP. I also recommend making it rather large -- 550MiB is my usual recommendation, for assorted technical reasons having to do with rare bugs and FAT sizes. That said, if you've got an existing installation with a smaller ESP, or with multiple ESPs, it's probably fine to just stick with it. In either case, Linux and Windows can share a single ESP just fine. I do, however, recommend backing it up early and often -- definitely back it up before installing a new OS. Because the ESP holds your boot loaders, an accidental erasure of it will render your computer unbootable.
If you need to re-install Windows, it may be necessary to "hide" the non-Windows ESP by changing its type code. You can do this with
gdisk in Ubuntu with the
t command. (Try setting it to 8300, which is the code for a Linux filesystem.) You'll also need to use
w to save the changes. Don't do this now, though; do it only if it becomes necessary in the future.