Yay!! I have finally managed to complete the game. For one minute, I thought I would never get passed level 9 on res 5. Thanks to all the hints I have read on here, I managed to beat the last level, and with an expert score.
Everyone is right, chaining is everything. The way I did it was put each category into groups:
Group 1 - Business women, hot shots and young girls
Group 2 - Seniors and college kids.
I would stand at the podium until I got a few people in line, then I tended to prioritise the more impatient, ie Group 1, and seated all of group 1's first.
I would stand at the podium until they were all ready to order then take all orders at once, serve all at once and then back to podium until they were all done and wanted checks. Then I checked, cleared tables, then back to podium, before seating next bunch of people.
Worked for me...thanks everyone