In my experience, any System between 7.0 and 7.5.5 would boot fine in either clean or dirty ROMs. I do it frequently on the IIx, which uses the very same ROM as the SE/30. Tried an SE/30 with clean ROM, too. You don't need to reinstall or ResEdit anything.
With a clean ROM, you don't need Mode32 either, but it won't hurt if already installed... by the way, in order to install it, just copying the extension won't do -- the use of the original installer is mandatory. The last version of it is compatible with all of the aforementioned System versions, not restricted to 7.5.5.
In any case, you have to enable 32-bit addressing on the Memory control panel. If you have more than 8 MiB of RAM, they will show up as Built-in memory; but the System will appear to "waste" most of it, leaving the same free space as if you had just 8 MiB.
With a clean ROM, you don't need Mode32 either, but it won't hurt if already installed... by the way, in order to install it, just copying the extension won't do -- the use of the original installer is mandatory. The last version of it is compatible with all of the aforementioned System versions, not restricted to 7.5.5.
In any case, you have to enable 32-bit addressing on the Memory control panel. If you have more than 8 MiB of RAM, they will show up as Built-in memory; but the System will appear to "waste" most of it, leaving the same free space as if you had just 8 MiB.