The 'grain" on plywood is the long way...so make sure that the table is built with the grain..that's how it's strongest. You can probably even get the lumber yard to do the cutting for you...they are pretty good about that. Just tell them you need a piece such and such cut WITH the grain. Yes, I also used the folding legs, but seems I can only find the square tubing ones now...old table is the round ones. Keep in mind that even though you are tall...you have to remember the height of the dog in this. I often sit on a chair when grooming the underside of the dog, and some of my dogs will actually lay down on the grooming table to have their tummy done...which I love. My table is against a wall in the house, so they have the security of the wall behind them. It takes a while to "learn" the grooming table if they don't start young and you have to be careful with the noose because if they leap, they are taking the table with them, and it's very scary for them.
To make carriage head bolts work through the top, you will have to have a bit of an indent for them or they will bump up under the matting. Mine is just screwed on from the bottom...and I check them periodically to make sure they are tight. (Much simpler because you don't have to figure out where to drill the bolt holes...you just set the legs up on the table upside down and screw them in
YOu can use a 3/4 inch screw and it won't come through. The other advantage to thicker wood...longer screws. ON the last table, I found 29 too high, so had the legs shortened, and if you find you need that, it can be done after.
on 3/4 plywood, five feet should not sag too much - it's pretty strong. But if it does, you could always put something to reinforce it. As to whether it's too steep...I always think...would I walk up that slope myself easily? MY young dogs would probably do 45 degrees for a cookie, but the older ones, or ones that are not used to it, would not. Coming down, however, yea, I think they would, but I don't have room for that much length in my dog room....