You could still use those cranks. Get single stack bolts and move the small chainring to the large spot. You may also want to flip the BB axle so the cranks are closer in for a better chainline.

Get some clips and straps.

Take out the chain adjuster screws in the rear dropout.

You can buy a fixed hub and use your old rim, but I would get new spokes. Besides, if the flange height, spacing, etc is different, the old spokes wont work. However, you may be able to salvage the nipples.