So...
MEKO A200, available ASAP, limited to 16 VLS, design is older and has less ability to keep up with changing times, likely easiest to Australianize (MEKO series designed to be customized, possible 9LV CMS is already integrated as the Algerians were considering it), crew is smaller than the ANZACs but not by that much (notional 120ish vs 160-180ish depending on how aircrew and similar are counted) which makes manning an expanded fleet more difficult.
MEKO A210, looks interesting and capable but at the moment not much more than a sketch on a beer mat.
Mogami class, avalible ASAP, limited to 16 VLS, likely harder to quickly Australianize than the A200 and not Australianizing it has it's own problems (either integrating ESSM into the Japanese CMS or adopting the
Type 03 Chū-SAM... then again, Japan might be interested in integrating ESSM anyway as they already operate the missile and it'd open up supply options from the US if things get hot... ), substantially smaller crew (quoted as about ~90 but usual vaguries over how aircrew and similar are counted) looks very tempting. Possible concerns about if Japan's attitude on military exports reverts to the 1950s-2010s?
FFM, likely avalbile later than A200 or Mogami (ANZACs more shagged out and fleet shrinking quicker...), probably 32 VLS, otherwise per Mogami but later arrival date might make Australianizing more practical. Might also be concerns about stepping on Hunter class toes...
Avante ALPHA3000, while leveraging off ALPHA2000 still has substantial changes (similar level of risk to A210), hard limit of 16 VLS and only a pop-gun, crew numbers unclear but Avante 2000 numbers (quoted as 60+32) look good, concerns about performance (relatively short range, possibly lower sprint speed), also concerns over previous bad experiances with Navantia.
Chungnam-class frigate, avalible ASAP, major complications as not just non-Australian combat system but totally different VLS, crew similar to A200, possible range concerns.
If wanting to go for a uniform Tier 2 fleet with hulls arriving ASAP I'd say as of now the A200 looks like the best bet. If considering a split order three Mogamis "off the rack" and then Australianized FFMs looks better (I'd say order a full 12 and sell off the Mogamis once FFMs arrive en-mass... or maybe a "reverse cutting out expedition" into HMNZS
Philomel to stop the RNZN degenerating to the RNZRC...).
This would be my choice, pick a hull that can take current ANZAC sensor, CMS and effector systems, plus another 8vls cells and a Phalanx and order them. No significant integration efforts, just bolt the systems from a shagged hull to a new shiny hull. That hull is likely to be a bit bigger, and may need slightly less crew to maintain it, but will avoid all of the system change and training issues of using new combat systems.
I’m not saying this will be easy, just easier and quicker than doing everything new and different.
Given the available hulls that sounds rather a lot like saying go with the MEKO A200...