Glad you are enjoying it.
Your starting problem may be down to the battery - my 06 plate one had it's original in it when I bought it in May 2016 and often seemed a bit unwilling to start, more so when warmed up for some reason. :?
A new battery in December 2016 fixed that so I'd have a look for any date stickers on your battery and go from there. As yours is an 07 it may be due one!
I've no experience of a 2.0 but my Z4 does have a higher idle speed for the first minute or two, so yours doesn't sound unusual.
Even on cold days I just start mine and drive it - but I never "give it the beans" until it has warmed up - that takes 5 miles or so IME.