I had a classic as my first car, and I paid through the nose for it (£1800 quid FC) - I just saved up. It wasn't much more than others were paying at the time for 'normal' cars. I actually got insured through a normal insurer because many classic insurers wouldn't let me accrue NCB, which was vital.
Consolation was that the 2nd year, with a year's NCB, only cost £550.....so it averaged out at £1175 for the first two years.
In both instances it was still cheaper than my friend on his Corsa with a 1.2, whereas mine was a 'proper' engine at 1.9. Regardless, there are insurers out there that will cover you but you'll have to pound the pavement and ring around
Anyway, if you can't afford to buy the insurance or the car without paying in installments, you can't afraid to run it unfortunately. If the trans drops out, there's an £1,500 quid bill - and what are you going to do while it's immobile? Who's going to foot the bill? Where are you going to put it? Etc....
Not being unkind at all, it's a great idea to have a classic as a first car - but something like this just won't be fun and will ruin you. You might think you can live with single-figure MPG as well but in reality, when you're standing at the pumps, and you've just put another £100 into it, you'll be hurtin'........Make a nice garden ornament though, until the grass starts growing over it
It would still only do about 10mpg, if you're lucky, on gas - it's not going to be cheap either way unfortunately.
There are much, much better choices for a first classic than that

Things that you could genuinely use and enjoy without having to worry about
I have to go to work but I will stick up some more 'sensible' suggestions later for you to consider, things that might be a bit closer to what you would want.