voicing a minor 7 flat 5? in a minor key?

On the minor 7th b5 I wouldn't put any extensions on it but on the dominant I would definitely use b9,b13...remember when you start altering a minor chord you start taking it from a ii chord to making it a I chord, this is in reference to upper extentions..ie: 7ths maj or min, 9ths,11ths, 13ths...but dominant chords are fair game for most anything....always remember to think of chord function ...as a for instance in Blue Bossa, when you're soloing...left hand voice...Cm69 use 3569, Fm use3579, Dm7b5 I use root pos.,G7 use 7b93b6...try it you might dig it.

As a guitar player, you should know which notes you're playing when you play a chord. All you have to do is find out which notes and play the exact same chords on the piano. But if you're too lazy to do that: Em: E, G sharp, B C: C, E, G G: G, B, D D: D, F sharp, A You can find the notes on a piano chart. I'm pretty sure you can google it.

playing them just standard is a greatplace to start.

somethin to take note on a half diminshed chord:

you can add an extension to any chord tone as long as it is a tone above that particular note of the half diminshed, this gets you some slightly more colourful choices.

as for the dominant, when resolving to a minor chord as this is the case altering the 9ths and the 5ths is fair game pending on the melody.

try it without the extensions first and experiment with the voicings for each inversion. I think you'll find that the harmonic interplay for the chords (half diminished, dominant, minor7th) has a unique sound with interesting leading tone resolutions, especially if you experiment with inversions and substitution patterns.