I think there has been some really good advice on this thread.
I almost know nothing about Kongo Zen or Shorinji Kempo (probably the closest I might have gotten to the later was some Aikido in university, which I imagine is only vaguely related ). The Buddhist tree is very big and has many offshoots and branches. I suppose this site is about some of the lowest branches closest to the trunk. There are many layers of Buddhist texts and later developments in the various schools. This is a discussion forum that is tagged onto the main project website: https://suttacentral.net/ that hosts many of these early texts/discourses in Pali (a language close or perhaps the same as what the Buddha would have spoken) and versions in Chinese or sometimes Tibetan or Sanskrit (in other early transmission lineages). There’s a lot of similarity between the versions in the different languages and so people can get a good idea of what teachings are really likely the earliest.
I suppose Theravada is the existing school that is most closely related to these. However, Theravada has its own later layers texts as well that it mostly treats as canonical: various commentaries, meditation manuals, Abhidhamma etc. The texts here are common to all schools.
Bhikkhi Bodhi’s In the Buddha’s Words is a nice overview of what’s taught in these early texts. Pretty nice for navigating for context within Buddhism if you never read anything else. Alternatively, online, I found the summary of the Gradual Training on the Access to Insight site pretty nice for getting an overall picture of all this when I first started reading these texts. Or the free online book Word of the Buddha, an anthology of such material, covers similar territory. I say all this because as you’re here, might as well give a quick idea of what this place is about.
You mention enlightenment. Different schools come with somewhat different ideas of enlightenment. In the early texts, enlightenment doesn’t come all at once (the model may well be different in form to Zen or Kongo Zen). There are four stages. The first stage, stream-entry, doesn’t really seem to be much associated with meditation at all. Generally, this seems in these texts to be the stage most realistic or practical for laypeople to aspire to. Some particularly advanced laypeople in the texts do reach the second (once-return) or third (non-return) stages, but it seems these are mostly the domain of monastics, exclusively so for fourth and final stage (arahantship). The third stage certainly seems to need some advanced meditation (jhana) and the fourth stage using this to remove all remaining subtle vestiges of craving.
I don’t think there is any description of some layperson going away, doing some meditation, and then coming back a stream-enterer. I think, in practically all descriptions, some person is described as contemplating or listening to a dhamma teaching, the mental conditions are just right, and this moment/opening happens, e.g. like the following From Ud5.3:
The Gracious One saw the leper Suppabuddha sat in that assembly, and having seen him, this occurred to him: “This one here is able to understand the Dhamma”, and having regard to the leper Suppabuddha he related a gradual talk, that is to say: talk on giving, talk on virtue, talk on heaven, the danger, degradation, and defilement of sensual desires, and the advantages in renunciation—these he explained. When the Gracious One knew that the leper Suppabuddha was of ready mind, malleable mind, unhindered mind, uplifted mind, trusting mind, then he explained the Dhamma teaching the Awakened Ones have discovered themselves: suffering, origination, cessation, path.
Just as it is known that a clean cloth without a stain would take the dye well, so to the leper Suppabuddha on that very seat, the dust-free, stainless Vision-of-the-Dhamma arose: “Whatever has the nature of arising, all that has the nature of ceasing.”
Then the leper Suppabuddha having seen the Dhamma, attained the Dhamma, understood the Dhamma, penetrated the Dhamma, crossed over uncertainty, being without doubts, attained full confidence
The early texts say that a stream-enterer will not be reborn more than seven more times (and only in good realms, human or above). The supporting four factors for stream-entry in the texts are:
Association with people of integrity is a factor for stream-entry.
Listening to the true Dhamma is a factor for stream-entry.
Appropriate attention is a factor for stream-entry.
Practice in accordance with the Dhamma is a factor for stream-entry.
Stream-entry seems to be mostly about getting sila (morality) and other virtues (like generosity etc.) to a good level and developing an experiential confidence (not just intellectual understanding) in the teachings. The advanced meditation stuff seems to be primarily for the later stages (particularly suited for monastics).
As others have said, lots can be done without meditation: working on morality, generosity and other virtues, regularly reading or listening to suttas, listening to/attending Dhamma talks (there are several monasteries or centres in the UK where you might be able to find people of a like mind or volunteer/help out at, listen to Dhamma talks or Buddhist chanting, doing some chanting oneself might be a nice practice too). Many modern forms of Buddhism are very focused on meditation, whereas in the early period, for laypeople anyway, it seemed to have been a lot less emphasized.
Meditation definitely isn’t always helpful. I suspect there have been quite a few little-talked-about psychological casualties from long intense retreats over the years. IMO some caution and gentleness is needed in general. This probably holds at least ten-fold for you. As people with far knowledgeable than more have suggested earlier, you probably really need to find someone with expertise in both Buddhist practice and is a qualified psychologist/psychiatrist with proper knowledge of your condition (psychosis I think you said). I reckon there are bound to be a number like that in the UK. I think it’s only someone like that who will be able to more safely and fully answer your question about meditation. They would need to know your full history. There might be some approaches that might be possible, if approached gently and cautiously, with an expert keeping a regular eye on how things are progressing. Or it could be it would be simply safer to stay away from it (leave this for your next life ).
Most of us usually have plenty to work on anyway (have plenty of imperfections to be straightened out). The world badly needs many more kinder gentler people. Meditation can be a bit oversold at times too. The example of a fairly well-known Buddhist meditation teacher pops into my mind now. I won’t give his name but he had some very popular books on meditation, with decades of seemingly fairly advanced meditation experience, that not so long ago was found to have been secretly diverting book sales over many years into paying for prostitutes (I suppose that was at least better than some other dharma teachers that have pressurized/manipulated students into sex). His wife, unsurprisingly, didn’t take all this too well and kicked him out (out of the dharma centre they were running also). Seemingly, he still has more more work to do on the basics! There’s a lot more to practice than meditation. One can build up a really solid base in the fundamentals at least.