As to the ad hominem arguments
All I will say is that you have actually missed the strongest one of all, you would love it, but I will let you to find it yourself.
The two important substantive points are
1. Pensions, who will pay the pensions of NI public servants, retired PSNI sergeants, and maths teachers gone to grass. His suggestion is that the UK govt will as it was to the UK govt they payed Tax and NI during their working lives. Not an unreasonable view.
2 Debt, the regularly quoted figure of £9bn UK govt subvention to NI annually includes £2.4bn debt servicing costs. This is the share of UK debt service costs attributed to NI. This will obviously disappear, a UI will not be paying interest on UK govt debt.
A UI may have to take on part of the capital balance of UK public debt, if that were to happen there would of course be a financing cost involved, although as the Irish govt can currently raise money at negative rates that might even
reduce the annual costs.
Here is a link to a response by Alan Barrett of the ERSI to Doyle's article.