Only been playing for 3 weeks so be gentle pls

Looking for some advice just to make sure i`m doing things right, for example

Barre chords... if i take D maj , move it up 2 frets and barre the 2nd fret does this become E maj ( as long as i only play the 4 strings )? and does this apply to any `open` chords, whether in minor etc providing i only play the right number of strings...

Also regarding power chords / 5th, the root note is always the note that the index finger is on?

Many thx
yes and yes except on the E5 which is ur second finger on the second fret of the A string and the A5 which u move down one string
On Barre chords- yes. If you take a standard barre chord like Dmaj (x5777x) and move it up 2 frets (x7999x) it is Emaj. But you can't do that with open chords, persee(shit I hope thats how you spell it ) A standard Gmaj (320033) will not become Amaj if you play it (430044) but it will if you play (431144) but I find that quite difficult .

Regarding Power Intervals (they're not chords because they aren't a triad) Yes the basic shape is index on root and ring or pinky on 5th like a standard G5(35xxxx) or (355xxx) where the ring places the octave as well.

Hope this helps you.