We managed to secure an allotment yesterday

I want to try and use the majority of the plot because there are a lot of plots at the allotments that are overgrown and scruffy and I want to convince the man in charge that we are going to keep up with the work on the site.
He has offered to clear the site of grass and weeds using 'Round up' which he says will have no effect on the soil or vegetables we grow but I'm not so sure. I have a petrol strimmer so I will attack the grass and weeds with that. I don't want it to turn into a mud bath.
Anyway back to the original title. I would like to put in a large crop of potatoes but there is no point growing a variety that is commonly available in the shops so what I am looking for is an interesting, good tasting potato that is good for boiling, mashing and baking.
It also needs to store well
over to you