It's not at all difficult or expensive to comply if you're a small business; the whole thing is pretty streamlined. You need to file accounts, but for a small turnover you can file "simplified" accounts which are just two tables. There is one subtlety - you can't be a limited company by yourself. The minimum is one director and one "secretary", but you can get company-secretary-as-a-service.
VAT is a separate issue - you have to deal with it regardless of whether you're a company or sole trader, if your turnover is high enough or you're selling digital goods (VATMOSS disaster).
Background info: https://www.gov.uk/topic/company-registration-filing/startin...
e.g. These people offer a full package for £70, which if your time is at all valuable is a good deal: https://www.rapidformations.co.uk/package/all-inclusive-pack...
- what UK taxes do you owe as a non-EU resident member of a UK company on salary (besides the obvious 20% of company income)
http://www.hmrc.gov.uk/manuals/rdrmmanual/rdrm10425.htm : implies you don't have to pay UK income tax, which makes sense. You'd have to pay your local income tax instead. I'm not sure how this applies to national insurance (what Americans call "social security").
- can you deduct your salary from company's taxable income?
Yes, companies are taxed on profit not turnover.
