For the Warp question, check out the Help docs on Warp, they aren't that bad. And of course, for any effect applied to a clip, the effect and any controls for it are displayed in the Effects Control Panel (ECP). So that's where the options for controlling the effect will be found.
Export settings are always in the Export settings options. Scroll down and if choosing an H.264/5 preset, there are a number of options for encoding found.
Upon the export stage, a re-encode will happen, there is no way not to re-encode after you have edited the footage.
Warp Stabilizer is an intensive effect, that should be used preferably on edited portions of a clip, not entire clips. An entire clip will likely have portions with camera shake that will never be used (e.g. the cameraman moving his hand away from the record button or the focus dial). So, for best/better results, use Warp Stabillizer only on edited portions you want to use. And even then, you may need to send the clip for a roundtrip to After Effects, as Warp Stabilizer VFX allows for far more detailed rescueing of clip portions that need saving.
Like others have said here, the Effects Control Panel is where you can change settings to any given effect.