Congratulations on the new bike.
10 speed obsolescence - hard to say, but I have 10 speed Campagnolo on my road bike which also went 11 speed a number of years ago and have no issues buying new parts still. My TT bike is running 10 speed Shimano Dura ace and have had no trouble buying Shimano 10 speed parts either...
11 speed wheels - can run 10 speed cassettes just with an extra spacer behind the cassette. Won't work the other way around without some fiddling i.e machining the freehub, using a 11 speed cassette with one cog removed or using a Campagnolo freehub wheel with their 11 speed cassette which I've heard this will run fine on Shimano 11 speed.