You won't need to go through immigration, but as CPH-Flyer said will likely need to go through security. I'd budget 30 minutes for the bus transfer, including walking from the arrival gate to the pickup point and waiting for the bus, and another 30 minutes for an absolute worst-case security line. With a 3-4 hour layover, that'd still leave you 1-2 hours for the lounge.

ANA's international schedule isn't so extensive to the point where you have several choices of itineraries and layover lengths, and their lounges are nothing outstanding, so I'd just pick the itinerary with the best price and most convenient schedule, in that order.