It is barely more than a sprout at this point so forget about any need to trim. And if being grown as a houseplant, you may never have a need to trim.

Eventually I'd like to outside

"Eventually I'd like to outside "

Then just leave it alone to grow into a tree. They require minimal pruning except to thin to allow sunlight to assist ripening. It will take awhile before mature enough to produce any fruit and fruit production will be enhanced with a second, different type of avo.

Prefers a frost-free, semitropical climate and enriched, well drained soil. Full sun and plenty of water to get established.