If you are getting 42k as the whole package, it is pretty good. You can get a decent apartment for 12k and a car doesn't even cost 6k per month [I suggest you to buy a car as soon as possible. Over here, buying a car is cheaper than going in cabs].
You can have an idea about apartments from the classifieds section of this website.
Food is pretty cheap here. So there shouldn't be any worries about that. Whatever you have in UK, we also have here :D
Get everything confirmed in writing. You can get a salary advance when you come here to get settled down. If you are Googling Qatar right now, you would see most of the posts about Westbay area. That is the most expensive area to find apartments. So, if your husband is working in the Westbay area, rather than finding an apartment from that area itself, you can find a much better place a little further away. [Hope I'm making sense :)]

Hope this helped. Welcome to Doha :)