Steeping is a process in which all the liquids combined to make the single
juice that you would like to eventually vape begin to cure together and act as a single juice, not as multiple pieces of of juice existing in the same bottle.
A good method would be after you have created your recipe and got all your percentages correct, assuming that you have already created a smaller sample bottle ~ 1ml - 2ml to test before creating a whole jug full, fill the bottle(s) with the juice you will be using then let the bottle(s) sit in a bowl of warm water immediately after filling the bottle for approximately 30 min - 45 min. Remove from the water bowl then shake the bottle vigorously for a few seconds then then sit for a day or longer to cure.
I've found that after curing the juice, store the bottles in a cool dark safe place until ready for use.
As for filling the empty attys, they are typically all a little different. Some will use a Syringe 13g 18g depending on viscosity of the the juice.
As for choosing an atty - that would be a matter of personal preference and dependent on the device you use. Each has something a little different to offer. There are a few sections in the forum that will most likely have the specific information you are looking for if you perform a search.
Hope this helps.... and welcome to the boards....
Peace-