Welcome to the forum OP - I'm on my 2nd Coupe and this one is Montego Blue. It has 86K miles on it and, No, it isn't for sale!
Replying to a post like this is largely why I am on my 2nd! :roll:
Anyway I don't know how much browsing you have done, but there is a buying guide here:- https://z4-forum.com/forum/viewtopic.php?f=2&t=21281
The Coupes all had the 3.0 litre N52 engine (apart from the M Models) which has an electric water pump that is prone to failure any time after 8 years - my first Coupe needed one at 9 years and 60K miles. The pump itself costs the wrong side of £200 before fitting so if you find a car that has had one already that is a bonus.
But these engines generally seem to deal with the miles pretty well - my daily is an E91 325i with the 2.5 litre N52 engine and it's on 134K at present. So I'd be more concerned about condition and history than mileage, especially as you plan to use it as a daily - buying a low mileage one and putting miles on it is likely to drop it's value quite a bit.
There were two versions of the Coupe, SE and Sport. The biggest difference is that Sport models came with M-Sport seats, SEs had "Sport" seats and there is a world of difference between them - used M-Sport seats can sell for as much as £1,000 a pair so buying an SE and planning to swap them doesn't really work out! But some SEs had the M-Sport seats as they were an option. The other differences are that Sport models have a black headlining and lowerered and stiffened suspension (10mm lower IIRC).
And on the subject of options there were quite a few items that were standard on 1 and 3 Series models but not on Z4s - things like cruise control, rear parking sensors, stereo controls on the steering wheel spring to mind.
Bi-Xenon headlights, heated seats and upgraded stereos are also popular options (plus cup-holders).
Anyway good luck finding the right one - I couldn't resist a photo by way of inspiration!
North West Surrey
Yours is bloody gorgeous Mr Tidy!