After reading the many comments on spoil boards and hold-down methods I am still a bit overwhelmed.
I have decided to use 3/4" MDF that are 3 3/8" wide and cut with a 3/32" by 3/16" rabbet on the bottom, this make a t-slot when spaced 1/4". Should I also add nut inserts or dogs or both?
EDIT: I should rephrase the subject line, it should read, “Work Piece Hold Down Options.”
Believe it or not, just straight MDF works fine. Go ahead a screw directly into it. If you need to, counter-sink or resurface any eruptions you might get from driving screws without pilot holes. Unless you’re dealing with stock that’s small enough to matter, it’s not an issue to have a bunch of holes in your spoil board. Another popular choice is 1/2" holes for dogs with cams, or wedges. I’ve seen those used very successfully with thicker stock like carving boards (most of the forces are going to be horizontal, although thinner stock, like metal sheet or acrylic, can get yanked up with upcut spirals).
Don’t overthink things, you’ll just make more work for yourself, and push back the finish date.
Ditto!
and welcome!
3rd for screws straight into the MDF. But with a word of caution. If you have 2 layers of MDF make sure your screws aren’t so long that they get into the second layer. I did that, a bunch, and it caused the top layer to “bulge” up from the screws entering into the second sheet. I resurfaced and everything is good now, but it did cause me some headaches on some thinner acrylic before I figured it out. Also I use “washer head” screws a lot, right on the edge of the wood/acrylic/aluminum. Holds down and side at the same time and works well.
I’d also say screws. I often use them to screw down wedges that clamp the workpiece.
I tried the inserts on my Primo, I have a vacuum table that I rarely use, only for really big pieces, I have T-tracks at the sides which I’ve never used… It’s always back to screws… I need to try those pegs one day… 
I’m a big fan of my pin nailer from harbor freight.
I’d love to have those. We don’t have them like that, they are always “self-cutting” which is kind of annoying for wood. Still works though, but makes huge holes. 
Personally I counter sink some screws into the spoilboard to the table itself. Next board I do I’ll probably make some bolt in options so I don’t destroy the table top. If you go that route and you choose not to surface, my board had a bit of flex with weather changes so don’t be afraid to do some in the middle as well. Just make sure the screws are lower than any bit should go so you don’t knock them. I do mine about 1/2 inch down of a 3/4 MDF.
