Hi,
I would suggest you get something with as many of the things you want on it already, i.e. 1275, disc brakes etc., so you can restore them to your satisfaction. This tends to be cheaper than buying a moke without them and trying to buy the items individually. However having said that disc brakes aren't as hard or as expensive to get as they used to be.
Roadworthy Blue denim seats are rare to get these days and on a fresh restoration old faded blue denim looks crap, so I wouldn't put too much value on original seats as you will probably get them recovered if you are doing a nice resto.
A Californian on the id plate is nice for resale, but if it has all the options that is what will really adds to the value.
The condition should favor what skills you or your mates have. For example if you or a mate is a panel beater you can get something a bit rougher in the body but has decent mechanical bits.
Terry