FFXIV Endwalker Summoner

Mechanically, not at all. You’re free to make the choice in any order you wish.

At endgame, it will be optimal to choose the order that puts the most into the buffs you are working with, although that may be different depending on your raid composition.

The other reason to choose is that Garuda and Ifrit have some restrictions on their spells with long cast times, so make sure you can stand still to actually cast them when you enter those phases.

They are automatic against an active target and are locked at a total of 4 Demi-Summon autos each. There is no longer a need to manage the movement of Bahamut and Phoenix.

In dungeons it may appear clunky with movement, however, for stationary targets they root in place and cast without you having to do anything further.

Yes.

Most buffs mirror from master to pet entities, as well as tinctures and food.

Until the release of Endwalker, no.

This will need to be confirmed for 6.0+.

/petsize [summon] [size]

where you replace [summon] with

Demi-Bahamut
Demi-Phoenix
Ruby Ifrit
Topaz Titan
Emerald Garuda
all

and [size] with

large
medium
small

e.g.

/petsize "Ruby Ifrit" "small"

All of the command arguments can be done with auto-translate.