[Fnoord]

1) You can disable and remove them. If you do not use them, and plan on not using them, do disable them. Example: I use Firefox, not Chrome. I don't have Chrome installed (I do have Webview installed, obviously). Example: I use Spotify, not Google Play Music. I disabled that instead.

2) You can install Android without GApps (and even with microG). For example LineageOS. You can even decide to use minimal GApps such as the nano variant.

[davedx]

Can you uninstall them without flashing your phone?

[Fnoord]

Yes, but not everything. Everything mentioned in the list of GP, yes. However something like GCM or Google Play, no. That's why you decide when you're flashing say LineageOS whether you want GApps yes or no.

I'd also like to note that disabling them does save up space. Not sure its all completely removed though. From memory, it reverts to an old version which was bundled with that Android version. On old phones, such space can be vital. Especially if you don't have microSD or pref not to use it.