I would very much ask you to wait until Google is on board with Windows 10 mobile. Which is not going to happen any time sooner. Because, there are only replacements as of now and in some cases(like Youtube, Maps, etc), there are 3rd party apps only available. Youtube is well covered. But for Google Maps, the only client available is gMaps, a 3rd party app, which is kind of a little difficult to use. So your best bet is to use Here Maps or Microsoft Maps.
Hangouts is mostly not in Windows 10 mobile. A few apps does cover hangouts too. Again, instead of hangouts, you can choose skype or many other popular IMs.
But if hangouts, Maps are your thing, it will be best if you choose Android or iOS over Windows 10 mobile for now. In few words, if you rely heavily on Google for anything other than search, youtube or gmail, it will be best for you to stay on Android or iOS.
I would suggest you to feel the water first(by getting a low cost Windows 10 mobile first) instead of jumping right into the water(get a high end Windows 10 mobile and switch).