No, sleep paralysis is not inherent to a successful WILD.

It's hard to explain how to know when to step into the dream. It's different for everyone, but for me, I just know that I am now far enough along the (epic) journey to dreamworld based on how everything feels. The HI and everything in general gets more intense the closer you get to a full-on dream. So, for me, I just know because of how it feels.

Once you know/suspect you are now in a full-on dream, you could try to move your physical body. Hopefully, doing so will only move your dream body. Once you get outta bed (assuming the dream starts there), you may find it helpful/necessary to do some stabilization techniques. One common way to do this that works for many people, myself included, is to watch while you rub your hands together. Using your other senses is advised as well.

When you get a chance, be sure to check out the tutorials on WILDing, WBTB, dream stability, dream control, etc.

Don't worry about the stream of questions. Happy lucids!