scrdest

I've actually seen at least a couple songs in RS that had two-note fifth chords. However, even then it's better if you hold it like a three-note power chord, because you'll want to use the pinky to mute the string to avoid it ringing out when it's not supposed to. One major advantage of getting used to three-note ones is that you can just add another note with the pinky on the next string one fret above the root (like 3554, low->high E where a power chord is 35/355) to get a third and as such a full-blown chord on E and A strings that is really easy to move and hold.

Well, since it got necro'd... the most practical and essentially foolproof way is to simply fire up session mode with only a metronome as backing, with Jam for no chord changes and whichever BPM you think you can handle and stick to the pulse. If you get bored, do beat divisions - two notes per beat, triplets, etc. etc. You might want to turn it down, since if you're doing 2 n.p.b. you are essentially playing at 2x the speed. If you are lazy, you don't even need to change the scale, since if you move the starting position up or down a scale note, you get the next/previous scale (well, presuming a diatonic scale - Harmonic Minor has its own set of scales from its transpositions, but you want to learn diatonics first).

Go with whatever you want to play in the end. Most Lead songs, easier ones doubly so, are almost indistinguishable from their Rhythm counterparts. And neither path is 'easier' in the end - the fact that you'll need elements of both notwithstanding, advanced Rhythm playing is as involved as advanced Lead playing, just in a different way and requiring different focus.

Something really important to keep in mind, if you plan to learn scales, which I suspect many guys out there actually don't use: you only need to learn the patterns on the E, A, and D strings, and there's only seven patterns on these three strings that all seven modes of major scale share (sadly, the seventh mode, Locrian, for some reason is not in Rocksmith for some reason). If, for example, you play a scale in A, so starting fifth fret, low E string, you go up the scale to seventh fret, D string, and you can repeat the exact same pattern starting on that fret if you raise it a half-step (a fret) up on B, because B is dumb like that. Or let's say you play again, A - let's say A major. Now, if you're trying to remember what to play if you move up to low E, seventh fret (so second note of the scale), it'll just be the 'default' Dorian pattern (5-7-8, 5-7, 4-5-7) - if you started with Dorian and started on the second note, the pattern would look exactly like Phrygian, and so on - the modes actually go in the same order as they are listed in Rocksmith.

I find the quickest way to strum an octave-shape is to use your index finger (the one holding the fifth fret on A in this case) to mute the adjacent D string by holding it at a pseudo-barre-chord angle, so you fret A on the fifth fret with the tip and mute with the side of the index finger around the knuckle closest to the top. Another way is to hold the 'full' (three-note) power chord shape and slightly depress the ring finger on the D string to make it into a frethand mute, but you run into a risk of accidentally sounding a harmonic in some positions. Basically it's the same thing, but you either use the normal D5 (5-7-7) or the inverted D5 (5-5-7, shows up in, for example, Peace of Mind) shape and mute the middle string.

Well, yeah, I mean, you obviously could do it, but would it work harmonically?

I'm putting this here because, honestly, I have no idea what to do with this question. So, when you write a chord progression, you might substitute a major chord for its relative minor (a minor chord whose root is two notes below the substituted major chord) or, for that matter, a minor chord can be substituted with a major chord by reversing the process. But could you substitute either with a relative diminished chord one note below/above for major and minor respectively? It sounds like it could make sense, but of course you'd get a very peculiar sound.