In the "Getting Started with Woodworking" video, the holes through the 4x4's were drilled from the back. That is, they start on the side opposite the precisely-positioned mark, and drill through to hit it. If they can do this, more power to them, but I can't drill through 3-1/2" of wood to emerge at a precise mark without a drill press - and not always then.
So drill the benchdog holes through the MDF layer. Begin by laying out their positions. You'll want these to be precise, so that the distances between the holes are consistent. The vises you are using will constrain your benchdog spacing. My front vise worked most naturally with two rows of holes four inches apart, my end vise with two pairs of rows, with four inches between the rows and eight inches between the pairs. Because of this, I decided on a 4" by 4" pattern.
When you're working with linseed oil, never -- I mean NEVER -- leave used rags lying around. Hang them up outside, away from anything combustible, and where there's enough air circulation to keep them cool. Or put them in a bucket of water, and hang them outside later. If you're just setting a rag down for the moment, set it out flat, without folds, on something non-flammable. Hanging outside in the breeze, the oil in the rags won't retain heat while they oxidize. For the oil to completely oxidize can take in a couple of days, if it's warm, or more than a week, if it's cold and rainy. When fully oxidized, the oil will be solid and the rags will be stiff. At that point, they're safe, and can be thrown in the trash. Toss them in the trash before that, and you might as well say goodbye to your garage.
Be careful. Single 24x60" sheets of 3/4" MDF are pretty easy to lift. A doubled sheet is manageable. The countertop - 24x72" panel of 1-1/2" oak - weighs something over 100 pounds. It takes real care to lift safely. The joined top - 3" thick of oak and MDF - is past the range that can be lifted safely by one person. Don't try. Get a friend to help, or rig a block-and-tackle.
I don't see anywhere you mentioned the over all length of the bench top. A piece of 1 1/2" x 25" x 8' glued edge oak at Lumber Liquidators costs $192 including tax. Two piece is almost $400! Would that be better if I use two IKEA 1 1/4" x 25" x 74" solid Beech ($99 each plus tax) on top of a layer of 3/4" Birch plywood. That would be 3 1/4" over all.
1. Cabinet Making and Millwork by John L. Feirer. I read this book cover to cover when I first got into woodworking, and its still my number one reference book when researching a project or technique. I believe it was intended as a textbook for a high school shop class, so it's laid out in great 101 style. It includes descriptions of everything from how sandpaper is made to best practices for shop math, and provides details for both hand and power tools.
Using shelving in your room or kitchen is a great way to arrange and de-clutter space… I know, such ground-breaking term it is. Do not write me off yet, I just want to show you how you can build some clean floating corner shelving that appears to have no brackets. You can create them at no cost, and the hardest part of the plan is figuring out what you are going to put on these shelves when you are finished.
Of course, few benches can be ideal, and this one does have some drawbacks. That being said, most of the disadvantages of this bench are minor annoyances rather than deal breakers. For instance, this bench does not include any kind of storage whatsoever. Though, it does have the option of adding numerous additional features like a storage area. Still, for the bench, you would expect a drawer at the very least, maybe a shelf below the main table area.