I am new to forums so please excuse me, I have had an allotment for a few years, and should know something, but I think I need to make lots of mistakes first.
If you are afraid that you will kill your plants with newly manured soil, just pop them in and feed them liquid fertiliser, I make my own with nettles and confrey, so I have just broken down the leaves put them in an old black bin added some water in 3 weeks it stinks but you dilute this up and you will have super plants lovely green beans you can use this liquid feed for your toms and salads, but I wouldn't apply and then pick them leave for a few days .At other times I used the comfrey leaves as a mulch on top.
An old chap who has a plot up with me, never does anything to his plot until may and every year he grows the lovest crop you can imagine, so you have lots of time so don't panic.
I think its the type of spud you plant, I tried picasso, another friend of mine used to plant when we had a full moon sounds loopy but it is something to do with the magnetic pull of the moon, I didn't do that I was just lucky to get them in. Give them space, and don't leave too many sprouts on because the plant is trying to do tooo much, and you get ditty one.
Good luck, get a digging party going you get your mates to dig and you supply fish and chips and a few beers, I was told of this just when I finished digging for the very first time, and thought a few friends would have saved my back.