All of your questions are related to what level of DIY (Do-It-Yourself) that you're planning to work in.. Will you be getting this published thru a professional printer? Or are you planning to make the parts yourself, down at a self-serve Print Shop.. And assemble the individual books yourself?
There are serious differences in the answers to your questions, based on this important facet!
>>Now 1st, what dpi do I scan by, what should the size be?<<
300dpi would seem a safe minimum.. A printer I worked with once, told me that 250dpi was more than enough, when doing 'Offset Printing' which works on a lines-per-inch process.. Many printers also offer a cheaper Xerox 'docutech' -style of Digital printing. It doesn't require files that're quite as high-rez..
I remember reading an article about Digital Chameleon, once. They were a Winnipeg-based computer coloring company that does(did?) a lot of the coloring for DC and Marvel. They used to swear by scanning/using 400dpi files. They argued that it gave you the best balance between "control" over the Image characteristics. While still maintaining a file that wasn't too large & unwieldy to work with.. re: Photoshop processing time, loading, etc..
I used both 400 and 600 dpi files in a Sketchbook I published a few years ago. Looking back on the pages, I really can't tell which ones were which, to be honest. And I doubt that anyone else could, either..
>>2nd, In Photoshop, what is the document size I want to work with? How large should the pages be? When I make a document page to put in two scanned pages what size should that be so it prints out 8.5x11 with a .5 inch margin? When do I add text and screen tone? When I resized it, or when its still large?<<
The "classic" 6- or 9-panel comic-book grid, is usually published at 6" x 9" dimensions. But you could make them slightly smaller or bigger, depending on your own preference.. Your 10" x 15" original art pages would need to be scanned in, at 60% scale. You can purchase handy 'Proportion Scale' wheels at your local Art Supply store, that'll help you calculate other sizes/scanning percentages, should choose something larger or smaller..
Most professional printers will ask you to set up the entire comic-book as a digital file document. And every printer has their own preferences. It's best to ask first, rather than wasting time creating something you will have to shoehorn into THEIR production protocols.. Find a printer. And find ways to keep it simple for them. There'll be fewer surprises for you, at the end of the process..
If you're using an application to put-together the entire book.. My experience has been that many prefer 'InDesign' or 'Quark'. Other programs like the old 'Pagemaker' (which I still use a lot) will allow you to assemble all of the Text Balloons and Screens that you need. If you're scanning in these elements as more 'original art'.. You'll have to make sure you do so, at the same Scaling ration, that you did for the other Art pages..
>>3rd, to make sure printing is nice and clean what size do I print off of? Do I print them as jpg or Photoshop files?<<
If you're outputting 'Master Pages' that you plan to xerox from, at a self-serve print shop.. You should probably print them out as TIFF files. But if you're assembling an 'InDesign' or 'Quark' document, the KIND of file is less important, than maintaining/streamlining the 'resolution' of your Image files. Some printers actually prefer 'Adobe Acrobat' documents, because it allows them to spend less time/hassle sorting thru Font Files, etc. 'Adobe Acrobat' documents use pdf. files..
It's always a good idea to have "backups" for all of your Image files. Don't send original files to a Printer.. they may lose them. Always use/send copies.. If you find printers asking you to "send" files via the Internet? Again, be mindful of maintaining 'resolution' protocols/formats you've been following.. JPEGs and PDF's travel over the Net more easily than TIFFs and other weightier image files. But if you can, it'd probably be preferrable to burn your entire comic-book document to a CD. And leave THAT with them..
>>Also, what are some other dos and don?t of this comic adventure? I?m very excited to finally put this together and give them away at conventions and my local comic books stores! <<
There's some pretty good reading on the subject of "Making Mini-Comics" over at Tom Spurgeon's website.. Much of it, relates to self-publishing your own comic-book. The weblink is:
I noticed in one of the recent 'PREVIEWS' (Diamond Distribution) catalogs, that Dave (Cerebus) Sim has rereleased his excellent 1997 "Guide To Self-Publishing" book. If you can find it at your comic shop, a lot of good info still exists in it! Though the self-publishing retail landscape has changed considerably, during the interim..
Hope that helps, a little.. Good Luck!