You can book the ATA flight either way. If you go through Pleasant, you can book it either with or without ground, hotel, etc. If you go through ATA or a travel agent, you can book the flight alone.
You can go to www.ata.com to book it. You can book it through an online agency like www.itn.net.
I would compare prices at the different locations as they may vary.
The "Air Cruise" flight (with a higher level of service in coach than most; you can read about it at Pleasant's site) leaves Honolulu for JFK on Saturday and Monday evenings. It leaves JFK to go to HNL on Sunday and Tuesday mornings.
If the flight goes well (and it apparently has been well-booked and Pleasant is rumoured to be *very* happy with them with excellent passenger feedback), Pleasant could easily add more per week. There is room for more utilization of the aircraft on the current schedule, which does two round-trips to ORD and two to JFK each week. As United is dropping nonstop Hawaii service from ORD, and Pleasant has just started similar "Air Cruise" service to ORD, that may be the first candidate for an increase in service. Depending on the maintenance reliability of the aircraft, ATA could squeeze up to 3 more round-trips per week from the one L1011-500.