I do a lot of coastal fishing in small boats - a 22ft I/O runabout at the moment, also a 16ft inflatable. I take the runabout out as far as 60 miles. But in truth it makes me a bit nervous! Help, and even communication, can be non-existent or at least very long in coming, at distances more than a few miles from shore.
Here's how I break down confidence for offshore use:
For simple survivability: 100% reliable flotation (and warmth) - if the boat has watertightness-weaknesses (things like sterndrive propulsion, open bow, low freeboard, a transom door, or scuppers/through-hulls w/o a quick means of accessing and stopping a leak), it's best to have backup flotation like a liferaft, or at least exposure suits for everyone on board. Most modern boats up to I think 26 ft are supposed to have positive flotation when swamped, but how many would want to rely solely on that if life were at stake? If your pontoon boat has independent essentially watertight hulls, you probably have that covered. I take an 8mm wetsuit w/boots/hood/gloves every time I launch the boat - staying afloat is job #1, but avoiding hypothermia is a close second even in temperate waters. Around here you die of cold before anything else. Plan on surviving many hours in the water.
Hand pumps and redundant, well-maintained, over-sized bilge pumps are great tools for keeping a minor leak from swamping a hull. In addition to the built-in pumps, I have a Rule 4000 with long alligator clips and outlet hose that can be dropped into any compartment or location as needed. If your engines aren't running, batteries won't last long so have a couple of those bicycle-style hand pumps - they are surprisingly efficient. A corollary is to know your battery circuits and switching, and to make sure they're set up and used so the risk of accidentally running down all batteries is nil. Take a backup marine battery not wired into your starting and house circuits, to keep your communications gear running should your in-built systems be lost.
For confidence in eventual help/rescue: redundant GPS and communication systems. I'd strongly advise a quality 25 watt VHF station and antenna, with at least one handheld backup (and another in the ditch bag, along with a handheld GPS). A handheld will not have adequate range if you're in or low to the water and more than a couple of miles from the nearest help. Even a 25 watt station may not reach more than 10 miles under bad conditions. Learn which channels the local fishing and commercial traffic use. You can get VHF radios with DSC, which is an emergency button that broadcasts your GPS coordinates. An EPIRB/PLB with internal GPS is also a must, and offers redundancy that is long-range and independent of the boat's batteries. A satphone would be a big plus for building confidence among the crew and your loved ones on shore. Aside from the satphone, none of this stuff is particularly expensive any longer. A broadcasting AIS might be another good option. For awhile, $100 cell phone boosters that offered 25+ mile range were popular around here but I don't hear much about them any more.
Once you have the basic equipment needs adequately and redundantly covered, the most important thing, as mentioned above, is the choices you make on the water, especially with regards to seas and weather. The ocean is obviously not like most any freshwater body and will regularly throw way more at you than any small boat can withstand. Around here we get big seas and winds, but typically not without fairly good predictability over an hours-to-day or so horizon. You don't want to be caught out in bad conditions - ever - so if you're in an area where squalls can develop with little warning, that's something to respect. In fact, until the seas get to 8-10 ft and closely spaced, I pay almost sole attention to wind. I find it a much more significant factor. Don't be the weekend warrior who tries to finesse the coming storm. Once seas are up, headway can drop to just a few knots. That makes for a long trip home with plenty of time for more to go wrong. Your boat looks very exposed to heavy sea conditions - how does that bow handle oncoming steep chop? Does it rise, or plunge? A friend with a very nice and otherwise seaworthy 29' Pursuit found out that following seas - mostly just wind chop - would ride up the swim platform and swamp the air intakes, killing his motors and resulting in a 25-mile tow back to port on a day that should have been routine.
Buddy-boating is an excellent insurance policy.
One last suggestion for diving - have a really long float line out, make sure every diver has good surface signalling devices (tall SMBs, flares, whistle, air horn), and for sure that someone is left on the boat who knows how everything works and what to do.
