Part Time instructors form the backbone of many flying clubs. The main thing that the club expects is reliability. Once you have some students they will need to fly regularly and you will need to be available for them. If you have a good ops person in the club they will find students whose schedule can match yours.
If you are working one day a week then about 150hrs/yr is possible. Don't worry about the hours though, you don't want to lower yourself to the 'hours building' motivation.
Leave the advanced instruction alone, at low instructional time no one will let you teach ME anyway. Your first objective after qualification is to get the FI(R) restrictions removed. Otherwise you will need to be supervised and that makes you less valuable to the club.
Everything you need to know is here
http://www.caa.co.uk/docs/175/Lasors_Section_H.pdf
Good Luck
RF