If your looking at 04 plate Espaces,the best advice I can give is seriously consider an extended Renault warranty(their called 'Harmony' I think).This will keep the car covered after the 3 year warranty runs out(subject to the usual terms and conditions!).
The main worry with DCi's is
failures,although it does seem to be the 1.9 that is affected worse than the 2.2.If you do buy one,have the
and filter changed more regularly than Renault suggest.The extended service intervals (upto 18,000 miles for some DCi's) are the prime suspect when it comes to premature
Apart from that,the Espace is a great car,and if you get a good one you'll be more than pleased with it.As with any second hand car purchase,there are always risks,but buy carefully and get as much advice as you can,and you can minimise these risks considerably.
Sorry I can't be more specific in answering your other questions,but there are quite a few Espace owners on the forum that will no doubt add to my comments.