hi - nice detailed answers by Cno and Al Ears.
1. Your ears should be the ones to make the final decision, not reviews and other people's opinions. So try to audition all the suggested gear.
2. Room size is important, also the music and sound type you're into - suggestions will be closer to what you need.
3. As the others have mentioned, most streamers have DACs in them, which are just as valid as their standalone counterparts. Also, there's several ways of doing the streaming. U can either (a) go directly from a PC/laptop through a USB DAC, then to an amp and speakers (or amp with integrated DAC, like the Nad d 3020), or (b) stream via your router, either wirelessly or through ethernet (better sound quality afaik if you go wired), to a streamer, then an amp and speakers.
I, for one, like the second option better, since it's easyer to keep adding wireless sources, like friends coming with their laptops etc and controling streamer with smartphone app, etc.The only downside (if you can call it that) is that most streamers can't be used as USB dacs (their USB ports are mainly for upgrading firmware or playing music directly from USB sticks/hard drives/iPods) - but imo that's a bit redundant anyway IF you have a router in your house - which most people usually do - since the streamer works like an ethernet DAC in this situation.
4. If I were on that budget (admitedly I'm a newly turned Naim fan) I would keep it as simple as possible and go NAS-->Naim Unitiqute 2--> speakers. The UQ 2 is simple, tiny, sounds great, has a plethora of digital inputs, radio and can later be upgraded with power amp if you find it underpowered (which you shouldn't). It also has an analogue input if you wanna add a turntable later. If you audition it and find it needs more control and excitement, add the NAP100 power amp to it and it will make a difference. I think this will be enough for a 15 sq meter room kind of deal. For bigger (and the 5k pound budget), Naim Unity2 is the way to go.
As for speakers, Naim partners very well with the Kef (LS50), Neat (Iota for small, or Motive 2 or 2SX floorstaners), Sonus Faber (toy tower or upwards), PMC and Totem.
Goodluck.