Okay, I might suggest sorting the list by selecting "Group by Most Likely" which can be found on the right side of the page, when you get to the list of birds. Almost of the birds you are going to report will be in the first two sections(frequent and infrequent), and there will be absolutely no problem reporting those without photos. If you report any bird in the last section, I would suggest(though eBird will not require it) adding a photo, or a comment telling how you identified it, how you distinguished it from a similar species, etc.
Now as to your other questions,
I like to add photo of common species from time to time just so people can see I am properly identifying birds.
So say that someone reports a Great Blue Heron to eBird, and I am interested in going to see it, if that person has photos of one or two other species on that checklist, I can see that they correctly identified them, and that probably they correctly identified the Great Blue Heron too.
It's not necessary to add a photo of every species, or even add photos to every checklist, but adding some, builds up confidence in you from other people, or at least it does for me.
Don't worry, nothing will be removed, sometimes things just may not show up for the public to see.
If you report a "rare" bird, the programing will automatically flag it(It will alert you to this, so there is not need to worry about this happing without you knowing it), and live person(called reviewers) will have to take a look at it, if you have a photo uploaded, and assuming it is correctly identified, there will be no problem, and it will be excepted. If it is wrong you will be sent a email, from the reviewer, asking you to change it to the correct species, at this point you can either change it, or you can not, and it will be left as an "unconfirmed" sighting, which just means it will not show up publicly to eBird. When a bird is unconfirmed it just will not show up on eBird for other people, like on the map of sighting for a certain bird, thing like that.
I hope that made some sense, and that it helped answer some of your questions!