Dish garden is fine as long as you group plants that have similar light and water requirements together, otherwise you might have trouble in the long run. Also check their dormancy times. In general plants do better in their own pots, but I couldn't resist to make a dish garden myself, they're just so nice xD!

Best to pot separately 'til one learns requirements & conditions of the plants (especially since one is a new gardener).

One can always place multiple pots together in larger arrangements, while still having the ability to remove them individually as needed.

Making sure the plants are compatible is very important, if you place different plants together & one is always thirsty and the other is like a Camel requiring hardly no water theres going to be a BIG problem.
All the advice already given should get you going the right direction but if you still like to experiment you can always gain the experience.

Greg