dgman

You don’t mention what saw you have. With the EX type saws like EX, Pegas, DeWALT and newer Delta saws, you can mount the blades higher or lower in the clamps. I don’t know about the other type saws like RBI or Hegner. The magnetic sheets are not that thick. I’d say try it and find out.

The larger the number the larger the blade. If you start with say a .number 3, a #2 and #1 are smaller. A#0 is smaller. A#2/0 means it is actually a #00 and a # 3/0 means it is a # 000. Keep in mind that different manufacturers sizes may not be the same as other manufacturers. Then you have different blade configurations. It can be very confusing for a beginner. My recommendation would be to try different blade sizes and types from different manufacturers to get an idea what to use. As a scroll saw instructor, I start my students off with Olson #5 skip tooth blades cutting 3/4” pine. 
Tell us what you want to cut and you’ll get recommendations of what to try.

I use FD Polar blades also in sizes 3, 5 and 7 depending on thickness and hardness of the wood. I stay away from reverse tooth blades because the thicker wood can't clear the sawdust from the reverse teeth which will cause slower cutting and maybe burning. Pegas MG blades are reverse tooth blades.