Shaun,
It sounds like you’ve got a couple of things wrong within your document. Let’s look at these quickly, one by one.
As for size, always talk to the printer. Different printers can print different sizes and with different bleed/margin settings. So its best to talk with them before laying anything out.
Secondly, the overset text is an error that pops up when you have a text box that has more text in it that is not being diplayed. Go to the pages it is telling you, highlight the boxes and any box with a little red + sign within a red box in the bottom right are boxes that have over set text. Most times, its extra paragraph returns that got over looked. However, are you using text threads so that text from one box flows into the next box naturally or are all of your text boxes independent of each other and when you need to adjust text in one, you are adjusting text in all of them?
As for the fonts…That’s a tricky one. My guess would be that somewhere in your file you’ve used a font or made an adjustment to a font accidentally that doesn’t exist. Meaning, maybe you told Garamond somewhere to be Bold, but you don’t have the bold face for the family. The real kick in the pants is that it could just be a blank space somewhere. The real remedy to this issue to know and understand how paragraph and character styles work and use them properly because your only solution is to turn on hidden characters and go through paragraph by paragraph and look for any paragraph that when highlighted, the upper left box that shows font and formatting goes blank. That means you have more than one formatting set to the characters inside of that box. Adjust from there.
Hope some of that helps. I would suggest if you are going to be doing a lot of InDesign work, that you hit up a few basic tutorials, get a book or take a quick class. InDesign is super power and awesome! I actually don’t do anything in Word anymore because I can write and format quicker in InDesign and it just looks nicer.
Good luck!
Mike