I think you kind of have to look within yourself and your own lifestyle when overstocking. None of us can really know what that's like. If anything I might tend to agree with Carlove somewhat in that your participation here on the forum displays a high level of interest and an ability to stick to things, so we'd hope that means you'd not have trouble maintaining the same high level of dedication on toward the end of the first year and through the second year etc. to not miss the vast majority of those filter maintenance sessions and gravel cleaning sessions. I really do think a high-interest forum person has a high chance of being a good fishkeeper like that.
One other thing probably in your favor is that I get the feeling that most areas in the UK probably experience fewer weather caused interruptions in electric power than we tend to get over there in the US. Here we tend to have wind or ice storms that take down trees, at lesst in some geographic areas, and then we might be out of power for significant stretches. It helps to have a really solid plan of action for power failures if you are overstocked. Anyway, my take is that these interruptions are fewer and shorter over there?
Plus there is the factor of it being a larger tank. I'm probably totally wrong on this (logic would dictate that I am) but I sometimes feel that some of the effects of overstocking are not linear in the sense that if the fish can move greater distances, it lessens the potentially crowded feelings for them (the logic would point to the fact that percentages of ammonia/nitrite in problem situations play no size favorites, but I'm thinking more of things like swimming space and ability to get some relief if an individual fish is "not feeling well" or such.)
I truly don't want to bias you one way or the other, I'm simply trying to present things to help you think through something you've not experienced before and have to project into the future a bit on, if that makes sense. I still think it's great to have one of our group here doing such a cool barb tank!
~~waterdrop~~