When I took my first (half) plot on, I thought it was more than enough until I got going in the 2nd year and realised that I didn't have enough space for everything I wanted to grow. No waiting lists at the time so when I enquired about vacant plots I got one immediately that was nearly 3 times bigger than my half plot but was heavily infested with all the evil perennial weeds you can think of (couch grass, nettles, bindweed, marestail, bramble). With no pressure, I tackled the full size plot whenever I had free time and as long as I was seen doing something, the slow progress was not frowned on. At first I grew only summer crops through weed suppressant fabric keeping the half plot for mainly root crops while I gradually cleared the plot and improved the soil and ventured on to other crops.
A couple of years later I finally got the plot up to full production, but it wasn't long before it dawned on me that I never had time to do other things. And some weekends I was torn between going to one or other plot, and I won't even mention the deteriorating state of my house. Then our site got a waiting list and although no-one was told to give up their multiple plots, there was no doubt a lot of pressure to do so. Before long I started to resent the allotment.
Last year the drought was too much as the heavy clay soil baked and was too difficult to dig over (I have arthritis in my hip and elbow) and I had to spend too much time rescuing the crops. When it finally rained, all the weed seeds decided to germinate at the same time adding to the woes. The final straw was an eviction notice on my big plot - with the cold snap in May, a lot of my sowings had failed miserably and along with some beds I was unable to dig over properly, there were gaps and the plot appeared uncultivated even though I had lots of other things growing.
I was able to explain the problems I'd had on the big plot which the council accepted due to the exceptional circumstances but it dawned on me that splitting my time between 2 plots (which were on opposite ends of the site BTW) had really been the main reason. I spent the next few months wondering what to do - both plots had good reasons for keeping but there was no doubt the big plot had the potential (and the space to grow the summer crops that I love) so I gave up the half plot and you cannot believe what a relief it has been.
So to answer your question - at the moment you are no doubt full of enthusiasm and providing your site hasn't got a waiting list as devonbarmygardener has pointed out, I see no reason why you cannot ask to take on the plot. Being a newbie has a lot going for you so don't let that put you off but my advice is to recognise when things get too much and when it stops being an enjoyment but a chore, then make a decision and choose which of the 2 plots is best for you.