What can you tell me about it, good and bad.
Would it be wise to stay in Casta Del Sol and travel to Granda and Seville for day trips? or is the drive too long?

Yes both Granada and Seville are doable by day trip, I did Seville fairly easily in a day although it was a bit of a push. Most people will say to avoid staying in Torremolinos although I quite like it and especially Benalmadena (close by) which has some wonderful fish restaurants on the beach. Nirje is the resort many will recommend but I also quite like Marbella. There are fabulous places to visit within and from the Costa del Sol.

costa del sol.
granada.

check out www.andalucia.com and tons of good posts here about sevilla and granada . do a search above in box for those cities, and regions.

the posts will answer most of your questions.

yes, you can do them both if you have about 5 days to spend, IMHO.

parts of the coast are too built up for my liking, but.. there's a place for everyone.

Very busy in summer, major european holiday destination.Hotels can be quite full.
Best to make nightstops in those cities, otherwise time is rather short to do sighseeing there.

Personally I would not stay on the coast. Many of the resorts are built up with high rise apartments and hotels and are not to my taste. Some of them are downright awful. Even staying a few miles inland takes you into what feels like a competely different country and, for me, the real Spain. It depends on what you want.

If you are set on staying on the coast the Costa de Luz is less developed but very windy at times.

Diz01