Nope it's ok, my Mac is always in sleep mode when I'm not using it.
Apple recommends though that you shutdown your Mac if it's not going to get used for more than several months.
As for the DVD drive, you could theoretically replace it yourself it you wanted to.
If your not going to get it fixed, it will most likely just die someday. It won't hurt anything else if it does, but the best thing to do is to get it replaced.
These people make excellent repair guides, and also sell replacement parts but those you can get elsewhere.
iFixit: The free repair manual