It wont work unless you have some welding skills and can make your frame larger to fit a 24’’. As for crank lengths when you get right down to it I think you really have to try them and decide for yourself, there are alot of mixed opinions.
Like chromizone said you can’t go 20 to 24. For future reference you can put a 20" wheel in a 24" frame (or just about any smaller wheel in a bigger frame), just wheel walking tricks would be harder and the min seat hieght would be higher.
As for the crank issue just get a bunch of steel cotterless cranks, they’er cheep.