Replacing MC panel with separate meter and service panel
Will this be an automatic transfer switch or a manual one?  If manual, you might be able to relocate a couple of breakers to make room for a mechanical interlock, there are many available and are code legal. They prevent the main breaker and the generator breaker being turned on at the same time. If a portable generator, you'll need a generator inlet to connect to. If a permanently installed generator, it'd be hardwired to the generator breaker. This assumes it's not a split bus panel, in which case, this wouldn't work AND BE DANGEROUS.
If an ATS... IF and this is a big IF!  I couldn't find detailed images of your meter panel combo, but IF (THE BIG IF!) the feed from the meter is wires and not a bus, it might be possible to run conduit to the ATS and rewire it to put it &quot;in front&quot; of the breakers.  Technically then the breaker part of the meter/ breaker combo becomes a sub-panel and you'll have to isolate the grounds from the neutrals, which might require some re-wiring.
What you're attempting is a pretty big deal, and my advice is only a suggestion. Probably Harp will weigh in with one of his &quot;novels&quot; and give better advice than me, but this is a starting point.
As much as I hate to say this on a DIY site, you may need to call a pro.