It would have been unlikely to have had a toilet when first built, but it appears to have been rebuilt, probably with one, later. Gas lighting indeed.
It's not possible at this stage to ascertain whether it would have ended its days as a first. It very likely did remain 1st, but we couldn't be certain.
It appears to have been withdrawn about 110 years ago, thus unless it had spent many years in store, would have probably worn GNR livery.
Very careful analysis of oldest panels on it may reveal livery. PM me about next time you're in Downpatrick and if I am up north and free I will join you and we can examine it in detail.