I agree with everything posted so far but don't need to rehash it. I don't see a post from Ken Hatch in here yet, he is very knowledgeable.
What wood working do you want to do? If you want to make turned ink pens out of fancy wood it might make sense to just buy a ready made bench and go - but if you start talking to pen makers you might find they are building their own benches too. I like making household sized stuff like book cases and blanket chests and comfortable chairs. Pausing those builds to make my own workbench let me develop as a woodworker so my next piece of furniture came out better. I am also in the early stages of making a timber framed tool shed. Making building sized mortises and tenons for my workbench build were part of making that spark.
Go to you local library and see what workbench books they have in the woodworking sections. Sit in a chair and thumb through them. Anything you want bad enough to get a library card? Anything you want bad enough to whip out your phone and go to amazon?
On my first work bench my sawhorses shifted under my laminated 2x4 before the glue set, so i ended up with a LOT of planing to do. Make sure you are gluing on a stable, flat platform. Doesn't have to be level, but it has to be flat. Also my first bench is using a $20 vise from a home store. My next (second) bench I am going to a leg vise and I am willing to spend what I have to spend for top of the line.
Drilling dog holes is fun, that is absolutely not a selling point on a premade bench. You could spend a few bucks on a mirror with a hole in it, a peg hole drillign mirror, or you could turn some S4S from a home store into three S6S pieces and make a drilling guide out of wood with a few finish nails.
One other thing you could do is search here, titles only, on the term "work bench" and after you read or just look at the pictures in all those search again on "workbench."
Recognizing this won't be your last bench is pretty insightful.