The dive computers available today are simply not useful.
This is something I strongly disagree with. Dive computers are very, very useful. They can't measure bubble or various saturation levels of different tissue types, but neither can you. The models they use may be idealized and only have a fixed number of compartments for the offgassing calculations, but they provide several other benefits that make them a key component of any deep dive. For starters they track your depth over time. Everyone drifts and bounced around within a range of depths even when you think you are staying on a fixed depth over some portion of the dive. The computer is sampling and adding the depth changes into the model. This enables the computer to be more accurate than you can ever be. If you disagree with its model then you can do some research into what it is using as its basline profile and either buy a computer that uses a model you like or adjust its calculations according to how you think you fit its model (several of the dive computers you should be looking at allow for this latter option.)
I am not talking about diving on some recreational computer, I am talking about using a dive computer designed for mixed gases and dive profiles with a ceiling. If you are doing mixed gas diving you need a computer that can be set with the mixes you will use and be switched as you switch. Maybe you are good enough or experienced enough to get away without a computer, but I have always dived with a hand-caluclated profile (with various bailout options and numbers) in a BC pocket, a mental model of where I think I am in the dive running in my head, and a dive computer that can provide both accurate and precise info based upon its own model of the dive and diver.
Look, I understand that technically-minded people want to believe that there is a "right" answer and that problems can be automated away. But the reality is that no one fully understands how decompression works and the mathematical models are fundamentally not accurate enough to be useful in the midst of a dive. Better to accept a certain level of uncertainty rather than believe a falsehood. Free your mind.
Having a unified team actually increases your flexibility. When all your dive buddies have similar equipment and training then they're essentially interchangeable (within reasonable limits). Solo sport diving is always and everywhere a bad idea. You need someone to assist if you get entangled or have a serious equipment problem. Plus it's nice just to have some company and another set of eyes to spot interesting marine life. If you can't find a qualified buddy then just skip the dive; there is nothing underwater worth risking your life. There have been too many incidents of solo divers ending up dead for unexplained reasons, because there were no witnesses and no one to help.
The dive computers available today are simply not useful. The fundamental problem is that a computer can't accurately measure bubbles and dissolved gasses in your body. All they can do is run some simple, idealized models (i.e. "first assume a spherical cow") which are fairly close to what a typical person will experience during a limited range of dive profiles. For example, the models I have seen — including VPM, RGBM, and others — fail to properly account for the oxygen window during decompression and so will stretch ascent times out unnecessarily. A lot of divers lack the scientific background necessary to understand the difference between accuracy and precision. A dive computer will display highly precise numbers, but who knows whether they are accurate? Despite their limitations, the mathematical models are useful for understanding the general shape of the decompression curve across a spectrum of possible profiles. Once you understand that then you don't need a dive computer, or computed tables. No one I dive with would actually try to reference a table in the middle of a dive. If you want to waste money on an expensive dive computer then go ahead, just don't fool yourself into believing what it tells you.
Helmets are unnecessary for sport diving; don't dive in places where heavy things can fall on your head. A light on your helmet will blind your dive buddy when you look at him, plus having things stick out from your head is an entanglement hazard. Bring snorkel in your pocket if you want; it won't hurt but I've never found them useful. There's nothing wrong with bringing a bag of tools when you need them but please leave the wrecks intact so the rest of us can enjoy them, too.