Just watch the chicks,
@tigger19687 . They tell you everything you need to know, and you'll learn to "read" them within hours, seriously!! It has seemed through the years that the folks who have the most trouble with MHP are those that try to "overthink" it all. Use what you have on hand for a frame....as long as you can raise it up somehow as the chicks grow and need less heat, and it will support their combined weight when they get up on top of it, you're golden. With mine, if I needed to raise it up because it was too low or they were getting bigger, all I had to do was pull up on the center of the frame, and I could do that in very small increments. If I needed to lower it, I smooshed it down a bit. Folks using a shelving unit of some kind have found that adjustable legs make a world of difference, and again, if you can set them up so you can raise or lower in smaller increments you'll be ahead of the game there too.
@aart has designed a really good system for doing that. I know she's not the only one, but hers is the name that always pops into my head first because she's actually been using a homemade heating set up longer than I have.
If they don't want to go under it (bearing in mind that you sometimes have to give them a little shove and hold your hand in front until they realize that it's warm there) then there's a good bet it's too warm. If it's too warm but not horribly so, they'll congregate right at the entrance instead of going under. Turn it down a notch. If they are too chilly, they pile up at the very back or at the lowest point of the frame, huddle there, and don't want to come back out. Ideally what you want to see is chicks popping in and out, climbing on top and snoozing or playing, and going under to sleep all night long. Chick behavior with MHP is dramatically different than it is with a heat lamp and one of the most amazing things is how little time they actually spend under the heat. We are trying to duplicate a broody hen here, and they behave just as they would if she was raising them, except they don't have to go chase after her to find that sweet spot!
Indoors I started the pad on 5 but I don't know what kind of control panel your pad has...is it "high, med, low" or digital? Outdoors I started it on 6, but you gotta remember that it was 20 degrees out there. In just a few days it was already down to 4.
I know it sounds like a lot of fussing with it, but really there isn't. My chicks were outdoors. I set up MHP, put the chicks in and watched them for about half an hour while I did other chores out there, and then made the adjustments I thought I needed to. I checked on them before I shut things down for the night. After that I checked on them when I fed and watered them. Usually adjustments were only necessary every week or so, and when you figure that the heat was shut completely off around the beginning of the 4th week and the brooder came totally out by the end of that week, that's what? ... maybe 3 adjustments? Yeah, like that.