Regardless of how much time you spend in the UK, your UK income will be subject to UK income tax at 20% / 40% / 50% as it is from UK earnings. You may get a Personal Allowance (around £6035 as a standard deduction) to set against that, but you'd need to check.

You should do a tax return each year by 31 Jan for the year ended on 6 Apr the previous year, in which you get credit for the PAYE deductions.

It looks like you have a combination of employment and self-employment (i.e. a trade) - I think that normally there is no tax witheld from business income (which you can set against expenses from that trade), but if you are an employee of the first business they will be required to operate PAYE on your salary.

One optimisation strategy might be to set up a company, but you'd need to take professional advice about doing that.

Finally, my understanding is that the non-residency rule is based on 180 days in any given year, and an average of 90 days of a number of years. However, this really applies in respect of non-UK income.