Is a four tank day realistic?

Yes with nitrox, a proper surface interval, and a shallower fourth dive. Most operators run the deepest dive first and step up through the day. Watch your no-fly window at the end of the week.

Can I dive without a guide?

Depends on the destination and operator. Many will let certified buddy teams dive unguided after a checkout dive; some marine parks require a guide. Ask before you book if this matters to you.

Liveaboard or resort for this style?

A liveaboard gets you more dives and remote sites. A dive resort with a house reef gets you unlimited shore dives between boat trips. Both work; pick by the sites you want to see.

Dive Enthusiast Trips: Maximum Dives, Best Sites

You have the logbook, the gear bag, and the itch. You want the most dives the schedule allows, the good sites rather than the easy ones, and a crew that gets why you skipped the spa.