A lot of good advice, to add my own thoughts I would go the cheap and cheerful route for a little while to get used the weight and power (if you go the Direct Access route), if you've never ridden a big bike the first time you open the throttle hard can be intimidating and actually put you off, which is the last thing you want to do.
If you are around 6" I would avoid a 400 as they are tiny and generally now quite old.
I personally would look towards a 600 Hornet, Bandit, Fazer etc, no expensive plastics to repair or replace in the vent of a mishap and more than powerful enough to get you in and out of trouble.
Nictrix do you ever go on YamahaR forum
http://www.yamahar.co.uk/index.php
Been riding since I was 17, started on a Kawasaki AR125, then progressing through a Kawasaki KE175, Kawasaki GPZ600R, Suzuki GSXR1100K, Kawasaki ZXR750L, Ducati 916, Kawasaki ZX7R and finally my current Yamaha YZFR1 which after thinking I'd found a cure for my Z4-itis discovered it had merely mutated into YZFR1-itis.
From this
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Still not finished with it, got a new Carbon Hex Oval exhaust and Wavy Armstrong discs to fit to it, then looking at starting a new project on something completely different, just don't tell the wife.