I'm sure some others here would have experince with them... I do not.
The NACRA site has some info:
https://www.nacrasailing.com/nacradownloads/Manual:
https://www.nacrasailing.com/wp-content/uploads/pdf/nacra-500-570-blast-i-17-i-18-f-18-i-20-manuals.pdfBasic questions...
1) Mast up is OK. Be sure the rig is snug and restrain the mast from rotating. Rocking back and forth will wear the rig and standing rigging faster.
2) Yes, it appears to go through the ring.
3) Would need the manual. May be tack on the pole and halyard on the crossbar. Unless that is for a jib furling system.
4) Yes, typically you loosen a shroud to de-rig and then re-tension the shroud when setting up. You may have to go back and forth from side to side to get it tensioned evenly the first time.
5) Likely that is just the luff tension after the jib is hoisted and locked on the ring.