You can get by with 1g no problem, especially if you're producing.
Macs are expensive, but extremely reliable, its an investment not a toy.
And yeah, if you have any other questions just feel free to ask, given the figures you posted regarding your buget its certainly possible to get a great setup with that kind of money (especially in the UK).
My suggestion is, think of the BEST POSSIBLE SET UP YOU WANT, then slowly pick apart at it until you've narrowed it down to exactly what you NEED to get started, then gradually upgrade over time piece by piece.
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