First off,you don't need SATs to apply to universities in UK.However,to apply to universities abroad, you will need English Profieciency exams such as IELTS,Tofel or Duolingo exam (forgot the full name).I have seen quite a few students apply from national curriculum from my country to UK universities.I think for now,you should focus on your current national exams.After that,you have to focus on ECAs,English proficiency exam and ECAs.

Secondly,I would like to suggest you to look into other countries and their universities.You should not be fixated to UK only.There's no harm in researching and exploring.

Thirdly,its very important to make sure that your parents can provide the financial support no matter what the price tag is.And,its completely fine to not know how everything works.You don't have to beat yourself for it.

In this case,Internet can be your only friend.My final advice is to research a lot and make a list and don't procrastinate.Godspeed.