Ok, to give you all the info you need would take ages to write out, so ill keep it quick.
Go to bodybuilding.com and check out all the training and nutrition articles. Its a very good site and you will find plenty of good info there.
The weights you currently have (25lb dumbbells) is not enough. You need much more weight and get a barbell too, and also a bench too perhaps. Again, bodybuilding.com will have plenty of exercises that you can use, and show you how to do them.
In regards to losing weight (bodyfat) on the bike, longer at a lower intensity is probably more effective than 10-15 mins flat out. But if you prefer the quicker, high intensity type then you can do it.
In regards to calories, it depends on your weight and so forth.