First thing you should do is set up iTunes. Do not synch, although if you do it shouldn't matter. Hmm, looks like you must attach the iPad to be able to do this... it will try to synch automatically, don't worry about it.
In iTunes when the iPad is attached you get synch options to set. For video's and music, point to a special drive folder that holds ONLY what you want to put on the iPad. So create these folders before you attach the iPad... just move the wanted video/photo's to those folders. Then set the options under the proper tab for the iPad to point to those. When you synch the iPad it will copy what it has as far as video/pictures to the PC and those that are in those folders that it doesn't have to the iPad. When you no longer want those items on the iPad, just delete them from the folders and on the next synch they will be gone from the iPad.
The Purchased Tab on the iPad's App store appears to me to show all the apps on the iPad. It appears to me that ones I've taken off the iPad are there with a down arrow for it. Ones already on the iPad have a 'hide' option when basically deletes them. Of all I have the Down arrow on I can't tell for sure if I actually paid for them or they were free. I have 320 apps and I'm sure 95% were free and they all appear the same to me. I know I bought a few games (Hidden Object Games) for the grandkids to play with me, and once finished deleted them, but since some were also free I can't be 100% sure these were the paid or free ones. All I can say is 'look' and see what happens.