Flying to UK via Dublin as an Indonesian citizen via Ryanair - Transit visa?

I want to buy two separate tickets for this route: Berlin to Birmingham, transiting through Dublin on RyanAir - it's the cheapest and quickest to get there. I won't be checking in any bags and it looks like Ryanair is exclusively handled in Terminal 1 in Dublin. There's a 2.5~ hour transit in Dublin between flights.

I have a long-term residency permit in Germany, and I just got my short-term tourist visa approved to go to the UK. I'm an Indonesian citizen.

Anyone have experience on whether a transit visa is needed for Dublin?

Specifically concerned about these issues if I don't apply for a transit visa: trying to board the flight to Dublin, and whether once I've landed in Dublin it will be possible to get my connecting flight or if the Irish immigration authorities will not let this happen. Also wondering if the fact that I'm buying the tickets separately is a problem (there's no website that handles this connection, I found it myself when browsing via Ryanair's website - and they don't offer tickets with layovers on their own site).

Flight is in 2 weeks so a little worried about time management. Thanks!