I did a similar thing to what you are intending.
Bought a Yamaha SR125 for 500 quid. Luckily I had a mate who had done his restricted licence the year before so took him. I let him ride it, when he had given it the all clear I took it out for a quick trip up and down the street. It was an awful bike, but I only know that now from the experience I have gained in the meantime!
Being honest with you for the amount of time you are likely to own it, I wouldn’t worry too much about “what” 125 it is.
[TONGUE IN CHEEK] If you can, get some daft bint to pull out in front of you, when you are travelling REALLY SLOWLY, a week after you pass your direct access, the insurance more than covered the purchase of my first big bike… But that is another story! [/TONGUE IN CHEEK]
What ever you do ride it slowly to start with!