This arrangement will be fine and you will notice that as the weather gets warmer, there will be longer periods of sunlight. Begonnias do need a good deal of indirect sunlgiht. They do great as containered porch plants. Cannas will eventually need more sunlight and so once the ground is ready, transplant them. I prefer to plant my rhizomes directly in the soil once it gets warmer.
Heat pads helps to speed up root growth and hence plant growth but it's not necessary. I think you don't need to have a lighting set up unless you become more interested in growing seeds and other bulbs. For the moment your set up is fine.

ianna