Internal limits are exact same as in official PFS3.
Max partition size: 104G (Can't be increased without making incompatible block structure changes)
Max file size is 2G-1. (4G-1 support won't be difficult, >=4G would require new block structure changes again) EDIT: There are some unused bits in direntry structure, using them for extra filesize field bits should allow file sizes larger than max partition, up to 1T or so.
Bootable or not bootable partition size or drive size depends only on device driver with PFS3AIO. Check for example http://eab.abime.net/showthread.php?t=61666
There is no filesystem side boot partition size limit. Never have been. It does not exist.