Paying up front is fine if you do one thing - pay by credit card, then the credit card company is liable.
As said, any good instructor will start you at EoC (i) and take you through ALL the exercises, BUT if the hours you have unlogged have been done sensibly then you should work through the first few exercises pretty quickly, conversely, these could have taught you some things incorrectly and it might take longer.
A "standard" progress might be -
Trial lesson (30 mins) EoC(i);
Lesson 2 (this and all other lessons 1Hr) - EoC(ii), intro to S&L (i);
Lesson 3 S&L(i) intro to Climbing and descending,
Lesson 4 Climbing & Descending, S&L(ii);
Lesson 5 Medium Level turns.
But as pointed out, your progress could be faster or slower than this depending on ability and other factors, and elements might be introduced at differing phases for reasons of progress/airspace/weather so this is a VERY general guide, and of course you would probably not be doing the trial (30min) lesson so that straight away changes the dynamics.