Very nice little project, Metrovik. I think small outfits like that have great potential, and they're simple to get going. You had asked for suggestions - your run-round loop is necessarily short, I can see, so trains must of course be short. If you use the West Cork Clonakilty brach, the Foynes branch, or the sort of trains that would have operated at one time into Fenit, Castleisland and several other places like that - little backwaters - a single six-wheel passenger brake coach will suffice as a passenger train. The forthcoming Hattons one is perfect, and will be available in livery suitable to the era you are depicting. I am thinking that you'd get one of these plus at least one, maybe two wagons, into that loop and you could still run a loco round it.
Another possibility is to have a modern laminate type of coach, like the brake composites (1904 & 1910) used on the Loughrea branch. The first of these arrived in green, which is appropriate to your era, of course.
You'd need to have a "tin van" if you're using any diesels. Silverfox do them, but need to be told to use a correct livery, as their CIE green livery is pure fantasy.
So, passenger coachyes dealt with, what about locos? A "C" class, or if after steam has ended, a 141; or in the case of steam, an 00 Works J15. Another possibility for steam is one of those (British) North Eastern Rly. 0.6.0T tank engines, which bear more than a passing resemblance to an ex-MGWR "J26". Just slap an overall coat of very dark grey over it and away ye go. A dozen or so Provincial Wagons, mostly goods vans, but maybe a couple of cattle and opens for variety, plus one of Provincial's GSWR goods brake vans and you've more than enough for a thing like that.
I like the overall roof idea, though I would echo the comments about it hiding the train a bit much......... Could be fiddly, too, if something's off the rails under it.