When you first start diving recreationally, and within your limits (like me) you will find that in all the dives you do, down to 18m, you can directly ascend to the surface without a mandatory stop in a pinch. The dangers of doing so are comparable at 18m as they are at 5, in that (as others mention) there is the problem of the air in your lungs expanding as you go etc.
Am I reading too much into it to think that you are wanting to stay at these depths out of safety concerns? If so, read up more about the sport. You've come to the right place to do that! There will be some disadvantages to diving as shallow as you indicate. Firstly, you will probably need to go deeper than that in your OW course, assuming you aren't taking it 1-on-1. Secondly, as you indicate, you may have problems finding buddies who want to just stick to that depth. Can your wife be persuaded to join you? I was the less-willing partner when my wife and I learned, and I found that soon all my nervousness vanished. It's such a wonderful thing to be able to share with a partner, and solves the need to find buddies! Diving isn't for everyone, though, and it's good to respect that.
What I am thinking you will find as you complete your certification is that diving, when done sensibly, is not particularly dangerous. And there is a lot of stuff that you might want to see between that 5m limit you are thinking, and the 18m limit that you will be competent to dive. Don't get me wrong - there is a LOT to see at 5m in many places, and as a certified diver you get to plan your dive and stick to your plan. If you only ever want to dive at less than 5m, then you will enjoy some great long shallow dives, and nobody is in any position to criticise the goals you set for yourself. But you will be competent to further than that and I think you might find it hard to resist
Take the certification process seriously. Find a good instructor, and don't take a course where corners are cut. Take a longer course, with fewer students if possible. And then - enjoy. If you are poorly trained, then yes, 3-5m depth presents significant dangers. If you have been trained properly, then those dangers have been significantly mitigated - but that applies to slightly deeper diving as well.
It is good to be going in with a cautious attitude. I was quite nervous to begin, and would rather be that than overconfident and cocky. I sure paid attention to learning all those potentially life-saving skills properly!
As others have mentioned, discover scuba is a great way for you both to be eased in to the experience to see if it suits you.