Getting the bike up the ramp is an easy two-person job -- one to steady the bike, and one to operate the come-along:

The person on the come-along can be an eight-year-old.
The length of the ramp would depend on the height of your truck and if you are loading from, ground level or have the suggest bank, berm, ditch, or even a high curb.
If you have two ramps the person keeping the bike upright can walk up second ramp and stay level with the bike.