I'm a beginner and use dumbbells for my chest. Started doing my chest and noticed
not only my chest was sore a day later but also arms. What other muscles do the
press/flies work?

I bike 30-60 miles a week at a pretty good pace already but i read that it is a good idea to throw in strength as well as flexibility to your cardiovascular work outs.
Now I am a very skinny guy with all the biking I do already, but is the biking, dumbbells and standard stretching sound pretty good? Should I throw something else?
I'm on a budget so i figured those things should suffice.

When I do dumbbell squats it makes my front thighs ache but not my butt. I am doing them to try to tone up my butt but I am not feeling it work in those muscles. Can anyone give me any tips as to things to look out for? I have my feet about shoulder width apart, work with 5kg weights and squat down to just above 90 degrees with a slight lean forward of the upper body.

I know plenty of leg dumbbell exercises but I would like to learn some upper body workouts for a person that is a little skinny.

I know lots of legs, shoulders, arms, and chest dumbbell workouts but not too many for the ones that give you a six pack!