Thanks everyone.

Looking into the S300 crank. The freewheel I had looked at was for a 1/8th inch so will have to get the 3/32 version, the Shimano MX30 maybe.

Not really sure about the saddle/clamp. I know nothing about this at all. Guess I'll just hope it fits? Do I need to buy a seat clamp separately?

As for the headset, I think the Scrambler comes with fork and headset.