I am more familiar with E53 spec and price variations than E70 and don't speak with E70 buying or ownership experience.
Personally if buying an E70 I would look to buy a 2008 car as the earlier diesel cars had higher emissions than the 2008 onwards cars and thus the annual road tax bill will be higher for the earlier cars. Not a relatively significant issue maybe but as values drop and these cars come into hands of folk worried by such the 2008 cars will IMO the ones that buyers lean towards.
It is ironic that many with plentiful funds to buy new quite happily pay tens of thousands of £'s when primarily motivated by savings on road tax and/or fuel that are insignificant when cost to change sums are factored. In the middle ground, many buying used cars under 5 years old seem less bothered re such issues, but once cars get into hands of folk who are stretching selves to buy and run then issues like annual road tax bill are once again relevant. The 2008 models were marketed as having E D - Efficent dynamics.
If after an E70 I would be mindful that a 7 seat option may assist resale later but would happily own a 5 seater if the price was correct. As with most cars colour and trim will usually, (not always), increase demand and price. Again it's down to preference but don't pay black and black colour/trim money for a burgundy car with caramel brown interior.
There is a tendency for folk in the UK to put Sport models at top of their lists but with the state of UK roads SE models may be plenty firm enough.....................I suspect ride and drive behavior may vary between cars depending what boxes were ticked when ordered new. Pre 2010 models optioned with sport pack had adaptive suspension. Another option was active steering. I have read a few comments re differences but am not able to advise you what to go for. A BMW dealer selling a used example will be able to tell you the exact spec and options from new but you can check spec of any car by calling BMW UK customer services on their dedicated spec info line.
As with many looking at used cars of a particular shape you seem to be pitching in at the bottom of the market price wise.......Be careful to watch out for bad cars as the damaged/repaired, flood damaged and problematic live with the low priced bargains. Old advice but with any used car ensure you do a proper HPI or equivalent check such as an RAC data check...........(I would not compromise with a cheap data check unless you have compared what info it gives you against the other two mentioned).
If buying at lower end of the market I would 1st look at a couple of nice ones..........that way you will hopefully be better able to be vigilant against any problems - especially considering your indicated intended budget.
As for buying a warranty in general : With any warranty it may be worth looking at what is covered..............especially on cars with higher mileages as many policies covering high milers can require high premiums &/or excess/owner contributions ( betterment) payments and that assuming the policies cover the part concerned.
The warranties marketed by BMW vary levels of cover..............even their "comprehensive warranty" states in their T&C's they do not cover "Any item that has worn out rather than suffered from a defect" I can't elaborate on this and for legal reasons I would advise others not to. They also state their "comprehensive" warranty will not cover vehicles with over 100k miles at time of warranty cover start date.
I am not against buying used, (my E53 has over 100k miles on it & was 4 years old when sourced used), but if E70 shopping with circa £16k don't expect to source a decent car easily and for a warranty to take care all component failure bills..............Apologies if the above seems negative..........You asked for advice & I have tried to give it honestly rather than leading you into potential expenditure you might not have fully factored.....Fwiw mine is now only worth a fraction of the value of a decent E70.
You mention LCI - In terms of engines there were various changes throughout the life of the E70 and before the the 2011 year change. Unless you know your E70's you will be hard pushed to tell the differences between LCI and launch models. Looking at side by side images on a 2007 and 2011 model on any used car website you will see the slight differences to front and rear....Once again not wishing to be rude but LCI pretty irrelevant in same context as £16k.
Oh and the early E70's were all SE's with the dynamic pack giving side running boards......I had to trawl these boards to find that info. The ED engine cars I mentioned were made from 7/07 and I think you can tell difference buy looking at flaps behind the front grills............
Anyone else able to clarify please ????
Out of my depth now - There are plenty of E70 former and current owners on here...........hopefully there might be one or two that can give further buying advice - Not sour grapes but I refuse to write an E70 used buyers guide if I don't own one
Welcome btw
