From what I remember they don't do the 'reach test' again in Dubai, but they measure your height so as to get a reading for your Body-Mass Index number.
If they've already flown you to Dubai then I doubt they'd send you back, unless it was due to a very serious medical reason or a huge breach of company policy. I honestly wouldn't stress about it too much.
Laptops...tend to be slightly cheaper here, but in the first couple of month you'll be without flying pay, so you'll have to wait before buying them. I think Macs are the same wherever you go, but the advantage of this job is that you get to shop all over the world, so you can be more choosy. Personally I bought my laptop 3 months after I moved here, and found it cheaper in Dubai than in Australia. But yeah, it depends on what specs you're after. Plus if there's nothing you like here you can wait until you get your annual leave or an australian flight before you can buy, there's not really a huge rush, esp since a lot of hotels we stay in have crew rooms with free internet anyway.