If your tv doesn't have ARC capability, don't worry about the other gear having it. It doesn't provide a lot anyways (limited audio codecs can pass) and often different brand devices don't play together nicely (I disable my ARC capable stuff as ARC tends to want to use an input on the avr I don't want it to).
I wouldn't bother with the HTIB (home theater in a box) system you're considering, but your if your budget is represented by the GBP 272/USD 350 price point, that is fairly limited and the quality relatively low in terms of the electronics/speakers/sub provided. If I did have to get an HTiB Onkyo tends to put a somewhat normal avr in their sets. I don't shop HTIBs nor am I familiar with what's available on your side of the pond.
I'd look at a standard avr (audio video receiver) with the connectivity you need (multiple hdmi ports) so you can plug your sources (dvd, sat box) into the receiver then connect receiver to tv. Add a pair of L/R speakers then sub/center then surrounds as you can afford them would yield a better result in the end.