No need to add anything yet, you can easily wait until the roots hit the reservoir.
But if you want, feel free to setup the initial veg feed, it's not like you won't do it in any case.
As to the amount of bubbles, you'll eventually want ALL THE BUBBLES. In the beginning, less will do, you don't want to blast teh new roots into pieces with too much power. Rest assured, 5litres/min into 2½gallons is *not* enough to do that. You need a lot of bubbles for that.