You must have been present in the UK three years prior to the day of application, so yes, you want to ensure you'll tick that box.
For referee, practically anyone can sign. You work don't you? Have an accountant at work? I've signed for many people.
Basically anyone who holds any professional qualification is "good to go".
‘Acceptable professional persons’ means:
accountant
airline pilot
articled clerk of a limited company
assurance agent of recognised company
bank or building society official
barrister
British Computer Society (BCS) - professional grades which are Associate (AMBCS), Member (MBCS), Fellow (FBCS) (PN 25/2003)
broker
chairman or director of limited company
chemist
chiropodist
Christian science practitioner
commissioner for oaths
councillor: local or county
civil servant (permanent)
dentist
designated premises supervisors
director or Manager of a VAT registered charity
director, manager or personnel officer of a VAT registered company
driving instructor (approved)
engineer (with professional qualifications)
fire service official
funeral director
insurance agent (full time) of a recognised company
journalist
justice of the Peace
legal secretary (members and fellows of the Institute of legal secretaries)
local government officer
manager or Personnel officer (of limited company)
member of Parliament
member of Her Majesty’s Armed Forces
Merchant Navy officer
minister of a recognised religion
nurse (RN, SEN or holder of a BA in nursing)
officer of the armed services (active or retired)
optician
paralegal (certified or qualified paralegals, and associate members of the Institute of Paralegals)
person with honours (such as OBE, MBE and so on)
personal licensee holders
photographer (professional)
police officer
Post Office official
president or secretary of a recognised organisation
Salvation Army officer
social worker
solicitor
surveyor
teacher, lecturer
trade union officer
travel agency (qualified)
valuers and auctioneers (fellow and associate members of the incorporated society)
warrant officers and chief petty officers