The DF numbering, even if it was originally a coincidence, is something Oda pointed out and and let appear in print over a decade ago, and works out in just such a way (like the numbers adding up to the ship) so it doesn't seem like it's a coincidence.
Naming pattern theories are crazy, (especially since multiple languages, first and last names are all in play) and Oda doesn't give a crap about things like birthdays, but someone having a 2-9 devilfruit can certainly consider it a factor in their favor. He does like making the bounties or number of followers in the fleet work out a certain way, for instance, or having the combination lock on the fridge be Sanji inbetween Nami and Robin. Oda likes his number tricks.
Though with both Kuma and Kinemon accounted for, we're running out of possibilities that fit. Kinemon is a real shame there given that its a completely non-obtrusive non-overpowered fruit that allows for lots of variety and gags.