Haha oooft fit?! You're such a manchester boy! Remind me of my boyfriend a bit, things are mint and fit, he says oiiii to everything and mate quite a lot, he's from Manchester too.
Anyway, welcome! You definitely save money on this diet, it's one of the positives about it.
Whey protein shakes are a definite no-no. They'll mess with the diet. If you want to keep working out, S&S isn't the best option for you at the moment. Otherwise, cut down the working out, stick with S&S and hit the gym and work on the muscle when you're done. You won't be able to have enough protein to build muscle whilst doing a diet like this, the two just don't go together. Work out too much and you'll do yourself more harm than good doing a diet like this. I can explain why in more detail if you're interested but most aren't so I give the quick, short version!
For nights out, vodka and diet coke is the best option in terms of carbs and calories. Diet is no different to zero in terms of carbs from what I know, you're just meant to stick to zero on plan cos of the citric acid but after a high carb meal I don't think you have to worry about a little citric acid!