Best way to make my site?

Hello all!
I hope this is the right place to ask this, otherwise, please advise me where should I look for help.

I own a small flower shop in my home town, and as a first step to publicize it online, I thought of creating some kind of prizes to give (like 5 flowers/ customized bouquet of flowers ….), for those who register in my website!

I was thinking something like:
the customers would have to register on the website (and a User ID would be assigned to them). Then, on a weekly, bi-weekly and/or monthly basis, one customer from those who registered previously, would be randomly picked and awarded that prize!
Their unique ID would appear on that page and they could claim the prize.

What would be the best way to implement this?
do you think this would be very difficult to achieve?
I have basic knowledge of HTML and DB, and created a website with WordPress previously (simple blog).

Many thanks