Migrating billing from FreeRADIUS + LibreNMS to Netxol One

Been running FreeRADIUS with a custom PHP billing shim for six years. Migration to CRM is greenlit but I'm nervous about the cut-over. Two areas of concern: (1) prepaid balance migration — we have subscribers with fractional-day remainders and I want to preserve them exactly, (2) grace-period rules that our shim enforces via cron. Anyone done this move and what surprises did you hit?