Hi and welcome.
I ran a C43 for 18 months and it was a great car. I still miss it now.
Easy to live with? Yes, it's a medium sized saloon/estate so it's practical, comfortable and being a Mercedes - very well screwed together. It was as happy pootling to the shops as it was eating up the miles on the motorway.
Problems to look out for? Well, unfortunately Mercedes of that vintage are known for rusting and the C43 is no exception. Make sure you look out for any sign of tin worm - body repairs don't come cheap. Most C43s on the market now have done a six figure mileage and therefore have got to the stage where things will be starting to wear out. Don't forget, this is a car that was £50K new - they may get cheaper to buy as they get older, but don't get any cheaper to fix. Don't consider anything that's been abused or neglected.
Fuel consumption? I guess it depends on your definition of terrible, but going backwards and forwards to work (5 miles each way) I used to get about 17 mpg, which isn't exactly great, but at fast motorway speeds it would turn in 27/28 mpg, which I think isn't too shabby for a car with a big V8 under the bonnet. It's never going to win any awards from the environmental lobby, but if that's who you want to impress, buy a Prius.
HTH,
Cheers,
Gaz