Good rate?

I useally ride my BMX to the local-skatepark/village most-days, it's about 5-7.5 miles.

I'm starting to work on my upper-body, but I don't have a clue where to start, when to increase and what not.

I'm planning on doing sit-ups, crunchs and for my arms a 4.5KG dumbell (Which is about right for me, as it's not easy to lift up, nor do I have problems doing so) - Also, any ideas on how to use a dumbell? Instead of standing there lifting it up/down.

Also, can you use a dumbell while sat down? :/ I've never seen anyone do it.

Anyway.

Where should I start? IE
10 Situps
20 Crunchs
30 Dumbells & methods of using a dumbell.

Thanks!

You should start with one routine just to a point where its stressing your muscles after two weeks on that routine you should go up a level, if you wish to gain more muscle. However, if you do not want to gain more muscle you should carry on with the same routine to maintain muscle size.

You should never push yourself far over what your capable of as this will damage your muscles putting you out of your routine which will delay the process of getting your desired muscle size.