My advice:
You'll sort out what to do with the boys. You'll either make them sluggas and choppas or shoota boys - unless you have long vision (maybe!) and either sticky
tac or magnetize the arms until you flesh out your army.
My advice though...
Assemble the bikes. Use them to kustom-build nob bikers. All the legs are fine, and some of the arms will go fitting onto the bikes to show them holding the bike handles....but turn those bikes into nob bikers. Diversify their wounds. In fact, bookmark this and do this later:
1. Painboy
2. Waaaugh! Banner
3. Bosspole
4. Powerklaw
5. Powerklaw + Ammo Runt
6. Powerklaw + Kombi-Skorcha
7. Big Choppa
8. Big Choppa + Ammo Runt
9. Big Choppa + Kombi-Skorcha
10. Normal Nob.
Put those 10 onto bikes, make them
WYSIWYG with magnets (my advice) so that you can change out their arms for different games / tournaments depending on what you want to run or have points to run. In terms of where to get stuff to make all this...
Painboy - He comes in his own blister; you can make a poor man's painboy by painting/gluing a surgical mask on a boy (cloth if nothing else) and painting it white with some blood spatter. Give him a slugga in one hand (pistol) and shave down a piece of sprue for the end (or a real needle) to put a needlepoint on it.
Waaaugh! Banner - these come in a box of metal nobs....maybe in the new plastic ones? Or you can use the banner from fantasy orks....if you need to, just use one of the bosspoles that comes in your battleforce boxes. Just make sure you use a different kind than with your bosspole, and glue some gubbins to it to make it look like more than a bosspole.
Bosspole - easy enough, there's plenty in your bits from a battleforce box.
Powerklaws - You should have a few of these. If you don't have enough, you can shave down a fist and glue three pieces of sprue into a scissor/klaw looking hand. Don't forget that the forums here have a trade section if you need to find bits.
Big Choppas - There should be pieces for a nob with a big arm with a big axe with a spike coming out of the wrist-guard and a chain going from the axe to the wrist. Voila - big choppas. You'll have two from two battleforce boxes. For your third big choppa, take an axe arm, cut the axe off of another axe arm, and make it a double-sided axe...something big.
Ammo Runts - Biker boys come with one of these - its a little gretchin on a pole that fits into a slot on the back of a bike.
Kombi-Skorcha - Talk to your friends at your
FLGS; see if you can get any Tau flamers or fusion blasters, or space marine flamer weapons...you can use these to convert into kombi-skorchas to stick on the bottom of a shoota. Alternatively, the new plastic nobs come with an actual kombi-skorcha.
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The reason I use this combination is because it diversifies all 10 nobs, for as little points as possible while providing the maximum killing power. Three powerklaws seems to be the balance for me, and kombi-skorchas let you dump a bit of template power into whatever you need it for. I'd never throw a biker nob squad at genestealers, but I'd definitely have them drive up next to them and dakka the crap out of them in addition to two skorcha templates. Kombi-rokkits don't belong with nobs; if your're going to shoot them at a vehicle, then the nobs have to assault the vehicle, which is under-utilizing the nobs; you have dakka guns and a big footprint that lets you multi-assault where you want to go.
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Anyway, that's mya dvice.
Current Armies: 
Invaders (Salamanders Sub-Chapter)
A few vairous scratch built models
Just getting started
A few models with more to come
Orks, 4175 points
9 klaws seems like overkill, to me. I1 vs I3/4 isn't a huge deal, since you aren't counting on swinging first at every target to win