I have 7 plants now about growing for about 1 week. They are all in 2 liter plastic bottles. Do you think that will be enough for the entire life cycle?

Also, should I use fertilzer at all during the veg period? If so, what's the easiest stuff I can buy at Home Depot to use? And what's the process?

Let me take a wild guess here, you're growing in soil. No those 'pots' won't be big enough. Unless you are planning to switch to some hydro system you wil want to get pots about 3 gallon size. DON"T DO IT YET.
It will take a while for the roots of your plant to fill a 2 liter bottle, its the wrong shape. Too deep, not very wide. Cut in half would be better. In addition, clear bottles are not good, you don't want light getting to the roots.
At just one week you may be able to transplant them into something smaller without disturbing the roots too much. Having seedlings in smaller containers encourage early root development, the roots spread laterally instead of just down. Jusy my two cents. VV

^^as VV stated to you, bottles are not well suited to grow in.
go to home depot and get black pots to replace the bottles, those pots won't let light harm the roots and rain excess water thru proper drain holes, i bet you bottles did came with those get standard soil or a soil mix with perlite or expanded clay, don't take one with fertilizer added to it! and get some reading do, your plants will award you for it

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keep the thumb green and the gun oiled, !

I hate to say the same thing but there is no way they will stay in those 2 liter bottles. We use 5 gallon buckets it works perfect. Obviously you don't want to start out with a huge bucket something like a milk jug is perfect for clones/seeds. You never want to transplant more then 2 or 3 times if you have to it causes a lot of shock and stress to your babies. Especially when they go into flowering you want to make sure you don't have to transplant AT ALL! Once your roots are poking out the bottom it is definitely time to transplant you want to avoid rootbond or mold. good luck, let us kno how it's going. Here is our babies.

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