why dont you just take the soil and dig the holes now and then when you come back in april you will only have plants and can probably fit them in your backpack.
fishing line,a compass? if you think you might get lost a compass might be a good idea I guess, and it might help you determine east, west, south and how much light a potential spot might get not sure why you would need fishing line.
the more light they receive the better, dont be to concerned with early or late light as there is usually something in the way of one of the other if the plants are not in direct sunlight for most of the day its probably not a very good spot and the plants will not grow or yield very well.