Things to consider, I do like them no larger than 4", I even like raising the itty bittys less than 2 ". The itty bittys are challenging to get food small enough, and in the beginning need more frequent meals. Larger ones sometimes dont acclimate as well to captive living, while smaller ones may develop the puppy dog personality over time. Larger ones almost always come in with internal parasites as they are more likely to have been fed dead, dying, and diseased fish.
As far as qt goes, 2 weeks does not give you 100%, even after treatment sometimes parasites can be stubborn. A lion can come in eating and seem fine for 2-3 weeks for developing questionable symptoms, like stopping eating, faded color or cloudy eyes. Then last more than a week up to a couple of weeks before dying. A qt needs to be for at least 4 weeks, whether just observation, or treatment. I have had stubborn parasites not clear after treatment, and needed to retreat.