Brand new to RV'ing life is a pretty big learning curve. Your dealer should do a VERY thorough walk through to show you how to use everything. Especially if you are not sure yourself.
1. Toilet will not work at all. The toilet is 12V. So breakers will do no good. You need to make sure the 12V disconnect by the steps is not off.
2. Rinsing out the black tank would not make the toilet work. Also be VERY careful when hooking up water. Too high of pressure can cause issues, so I recommend a pressure regulator to no more than 40psi. Also, the red/blue lines under the sink are not "vent lines" but likely supply lines. So maybe they were loose...but that also tells me you are not set to tank flush, but supply. Are you sure the black tank is filling???? What makes you think that?
3. TV's will not work on antenna??? Do you have the antenna power booster turned on? Did you can forOver the air channels?
4. DVD will not play. you mean not at all? Or not on the TV? Did you change the input of the TV to HDMI 1 or HDMI to the DVD source?
This might help as well. PS. don't get overly confused by this video. This is NOT an Isata 3...so you may not have some of the equipment. BUT, it does walk you through the over the air antenna and the booster switch.