@Chalfie
Given that you don't own the Apple TV or a screen yet (but I assume you own an amp and speakers):
Buying a TV is a lot cheaper than a computer monitor as the resolution requirements are lower. Even a 4K tv can be bought for around £500. A second hand 40" HD TV will be around £250. A serious computer monitor of any decent size will be way more than that.
A monitor is going to be too small. 40" is the minimum size you want to be thinking about for TV viewing as you're normally further from the screen.
Assuming you have decided on ATV as the video source then you'll have to suck up the fact that this means more than one box. Most of the time these boxes are small. I use Gorilla tape and stick them to the back of my TV screen so that my space is uncluttered.
If you don't need the new features of ATV4 (games, Plex) then get an ATV3 for £40 as it has an optical audio out. you will need a optical (Toslink) to RCA adapter. I just posted a link to one this morning. Otherwise yo need a HDMI to RCA. One was posted a few pages back when this question was asked recently.
@Chalfie
Given that you don't own the Apple TV or a screen yet (but I assume you own an amp and speakers):
Edit: what @mashton said
Preferably don't TYPE IN CAPS and perhaps think a bit more about what information you actually need (and how to frame that question) before posting...