Your question is very difficult to answer in such a general way, but I will do my best. Rock is often the Pentatonic, and Blues scale. Trust me though, if I leave it there, I am being irresponsible to the deeper question you are asking that I believe you may not be aware of. Please read on with a fresh open mind, without pre-conceptions.
The scales tend to be the same in just about all idioms. Remember TENDS. My first suggestion would be to simply copy the things you already hear on recording whether they may be Rush, or Christian music. Everything starts with sound. The people you love TEND not to think in terms of scales. Scales are simply an organized series of notes that accompany harmony. Even Bach would improvise those amazing lines to harmony before he dictated many of them. The method of musicians starting with scales as a compositional focal point seemed to begin in the 20th century. Of course their were others, but one could often hear a trend in the writing.(12 tone row method of writing). Your question seems to indicate that you are not starting with your ear as home base. With that being said, you are well served to study scales in a very deep way. Knowing scales up and down will usually yield nothing. You must brake them down into different patters like broken 3rds and 4ths 5ths, (you get the idea) find every option that you can come up with. But remember the scales only serve as a kind of Syllabus to the sounds that MAY be useful. Now that I have tried to manipulate your thinking,
lets make it simple. (did I brain wash you?)
Simply start here:
1. Copy by ear the stuff you like
2. Learn scales like maj min blues scale, modes, pentatonic scales, and THEN see if you can connect
them to the tunes, and licks you dig. Often you won't, then ask specific questions about that particular scale related to the chord.
3. Keep asking questions, and perhaps find a great teacher in your area to clarify for you what you
have read on a one to one basis.
As far as slap bass goes, you have an endless resource of vids! I think it would be great to check out Anthony Vitti''s lessons on You Tube
and post some questions for him here on this forum. But remember to use your ear first!
I know this is a very general answer, but I trust it will yield the results you want in a much more meaningful way.
And lastly, all music has typical riffs or cliche's, you will hear them over and over.. Learn them.
Let me know if this was helpful, and report back. I hope it will bear fruit for you!