Tips for a Menagerie

Yes I have read the hermetic projects book for this. Each time I reread it the more I want to make this character. I have a few things I'd like to have input from the community on as well as any potential tips on what NOT to do so I don't dead end myself by spreading myself to thin.

I'm a little uncertain in regards to certain aspects of the formula to tame a beast. It says Re(Fo) but I'm not really certain what form other than animal would come in use when trying to tame beasts. Any suggestions on how to diversify and creatures that would make use of the diversity would be appreciated. I'm also facing an issue in regards to being unsure of whether I should be focusing on a particular species or if diversity is capable without to much difficulty. I was debating taking a magical focus to specialize but I'm not sure if I should or if I should instead spend the point(s) elsewhere.

I feel like my biggest hitch in finishing my character's virtues is trying to determine how specialized if at all I should be when I'm looking to establish a menagerie. Personally I would prefer to be as diverse as possible but am still unsure over forms required and the potential usefulness of a magical focus. Any and all suggestions and tips would be much appreciated.

When it comes to a magical focus, the Major ones of "Birds" or "Mammals" are in the ArM5 main rulebook, and will help you with a wide range of creatures as well as with binding a familiar.
"Legendary Beasts" is a minor magical focus listed in HoH:MC, so you can take that if you're specialising purely in legendary creatures.

The Re(Fo) bit is straightforward - if the creature is mundane, it will be Animal. If the creature has Might, what form is it aligned to and what sort of vis would its corpse leave behind? A mythic sea creature which has Aquam in its corpse would count as aligned to Aquam, so your ReAq total is most appropriate. A baby phoenix or dragon might be aligned to Ignem. A great many beasts without particularly great supernatural powers would default to Animal.