I wear the same size as my normal shoes in all brands apart from Adidas. There's no substitute for getting them on your feet and trying them. Don't go on what other people tell you. If you ever go anywhere that says they don't make the 1/2 sizes then I'd take your wallet elsewhere.
I'd give the Garmin teccie guys a ring. I've spoken to them once or twice and found them very helpful. I don't think Garmin are doing any software/firmware updates for the 405 but might be worthwhile checking you have all the latest releases downloaded.
I'm in a similar position. The 405 has tons of features on it that I don't use but being able to download training schedules and be prompted what to do during a session is one that I have used. Think I'll probably get my 405 repaired.