Its one thing to get a list of keywords, but finding the difficulty of a keyword is BLOODY DIFFICULT!!
There are lots of tools out there which claim to tell you the difficulty, but when comparing a large sample of difficulty metrics, you WILL find there is little correlation between any of them.
Keyword planner is the place to start for finding keywords, UNF is great for getting up to 30k keywords in a short period of time.
then finding the difficulty... SpyFu probably has one of the best difficulty scores, but it does not always have every keyword in its database, plus it only allows 1 keyword per search.
Some difficulty metrics to avoid: UNF, Traffic Travis, Wordtracker, Google exact match results... Yes.. These are ones you may have thought would be good.