Hi Nicola
I went to Cambodia and Vietnam last year and liked it so much that I am also going back to Vietnam on 20th April (the itinerary is slightly less hectic, and we are staying longer in places that I want to revisit).
My Vietnam tips are :-
Money – US Dollars are accepted everywhere that you go. Try to get small denomination US dollars, especially $1 bills. Prices there are generally shown in Vietnamese Dong and US dollars. The Dong price is usually slightly lower than the Dollar price (they round-up the Dollar price) but if you buy something priced as $3 (say) with a $5 note you will probably get change in Dong. This way you naturally collect Dong which can be spent during your holiday or used up at the end of your holiday as tips.
Hoi An – this town oozes with silk/material shops which will make bespoke clothes (tops, blouses, entire suits) with something like a 24 hour turn-around – guys, yes they do men's shirts etc as well. If this is something that interests you, get yourself measured up there, or bring a favourite top (or whatever) and get it reproduced. Prepare to haggle, but this is a chance to buy something special to remember your holiday by.
I've posted a similar reply to Phil on the "ask you editor" community page in case you think you'r having double vision;)
I look forward to meeting you (only a week to go !!)
Kind regards
Joyce