I'm planning to buy irish-domiciled ETFs, with the aim to hold onto them long term. If I'm starting slow, eg.USD 2000 starting capital, which broker offers the lowest fees?

Irish-domiciled ETFs are mostly listed on the LSE, so you will need a broker that supports LSE. If you plan on a lump sum investment and not investing on a regular basis, Standard Chartered will probably be best for you.

Interactive Brokers has better foreign currency exchange rates and lower commissions, but charges 10 USD minimum commission monthly unless you have over 100k USD in assets with them. Saxo has high foreign currency exchange fees (0.75%), high commissions (min 8 GBP) and custody fees (0.12% p.a.). You may want to consider switching to Interactive Brokers in the future when your investment amount and frequency increases, where the costs saved will outweigh the minimum monthly commission.​​​