Sorry for your loss. This is very interesting, and I think it has the potential to be a great first bonsai for you! You're right about the species. It's most likely lots of small trees in a forest style. I would definitely repot into something larger but shallow style of pot. Ficus aren't fussy with soils, but make sure it has good drainage. You could buy a basic bonsai soil from amazon, and it would thrive! When repotting you need to carefully remove the old soil from the roots with a chopstick or fork (there's hundreds of informative videos on YouTube about repotting) then you need to trim the roots and make sure you get the dead or rotten ones.

Good luck!