Congratulations!
I'm very excited for you.
I have one too which I got in June.
We were strongly advised not to rotavate as it chops up and therefore multiplies the weeds. If you are going to dig them out first you will do the job of the rotavator yourself.
If you poison first with something like glyphosate ( brands like Round-up) you have to make sure it kills all the types of weeds present, then leave it a few weeks to work before you could rotavate.
There is a question about the organic-ness (?) of glyphosate - it allegedly neutralises on contact with the soil.
If you have a lot of weeds you may want to strim first ( if you have brambles def. use a metal blade strimmer), wait for regrowth, Round-up, wait for it to work then dig or rotavate.
You can plant safely according to RHS after a couple of weeks of using glyphosate.
We strimmed and covered the lot with black plastic and black membrane - whatever we had really. If the ground is wet under you can use black plastic to rot it down but if it's dry membrane lets through water so is better. Allplas
online is very cheap place to buy either.
Try getting a shed for FREE from Gumtree.
Bosch make a battery powered mower, seen cheapest on ebay about £189. Perfect for an allotment.
I'm opting for membrane and bark chipping paths as we get chips delivered free to the allotments.
This is my blog I have started to keep a record of what we do. It's only the beginning for us too!
I could go on all day.