Biggest tip I can suggest is be extra patient.
IRM's wagon packs are excellent value, and every Black Friday, they hit us with something even better.
Everything will be re-run eventually, whether locos, wagons or coaches.
Going even more buget, there is a thread on British locos that can be disguised as Irish locos here:
https://irishrailwaymodeller.com/topic/11073-british-locos-and-stock-that-can-be-disguised-as-irish
Hatton's quite frequently have open wagons, closed vans, containers, Mk1 coaches, Mk2 coaches etc very cheap.
The other day, they had brand new Mk3 coaches for £15 GBP each.
All of the above would be ideal candidates for re-painting.
Bachmann N Class Moguls show up in SR livery and BR black livery for £50 to £80 at Hatton's from time to time. De-badge with a cocktail stick and you have a relatively Irish loco.
And, as you say, @leslie10646's wagons are brilliant value for what you get!
I guess there's going to be a trade-off between budget and realism, almost on a linear scale at the centre, so the budget you want to keep to will determine how realistic you can go.
@Sean posted a thread on budget Irish modelling, back in 2019 or 2020, prior to his workbench thread, but I can't find it at a glance.
One could also look for non-runners to repair, as in this thread:
https://irishrailwaymodeller.com/topic/12359-wanted-non-runners/