6 Destroyers, 20 Frigates size, and 12 Corvette/OPV size combatant is quite formidable for Mediterranean. However I suspect will be challenging not only in Budget but also in manning to be done in a decade time.
I don't see where they'll all come from. Start with the destroyers: currently 3 (down from 4), of which the 2 Horizons will have life extensions, &
Francesco Mimbelli will be replaced by 2 DDX, making 4. No plans I've heard of for 2 more.
Then the frigates & frigate-size ships (i.e. PPA/Multi-Purpose Combat Ship). Currently have 8 FREMM (10 built, 2 sold to Egypt) & 2 ancient Maestrale class, with a 9th Fremm undergoing trials & a 10th fitting out, to replace the Maestrales. In addition, 2 FREMM EVO have been ordered, making a total of 12 FREMM frigates - but it's been reported that Italy has formally notified Greece that the first 2 FREMM will be available to buy when the 2 FREMM EVO are commissioned, which if the Greeks bite (they're reviewing the offer) knocks the frigate total back down to 10.
FREMMs for Greece
Plus, of course, the frigate-sized PPA/MPCS, of course, but to have a total of 20 frigate-sized ships would require 10 of them, & there's no plan for that. The number's still 7. 4 currently in service (6 built, 2 sold to Indonesia) & 1 more building. 2 more will be needed to reach the originally planned 7.