The secret of legato is muting and articulation: since your right hand is not doing much you have to use your palm to mute the lower strings and your fingers to mute the higer strings. The articulation af you left hand has to be relaxed but solid so it takes alot of practice but when you are doing correctly you can play for hours. So to practice left hand use a clean sound and for muting lots of distortion(duh). one of my problems is that somtimes doing legato i don respect the duration of the notes(my fingers run for themselfs)

Sweeping is not one of my favorites but the key is like you said !picking! there is not a correct way to do it but here is one exercice

e----19p15---------15-19p15-------- D down
b----------17--17------------17----- U up
g------------16------------------16-
........D......U..U..D....D...U.......U....U PICKING
.......(U)...(U)(D)(D).(D).(U)....(U)..(D) I use this one

e----17p14--------14-17p14--------
b----------15---15----------15-----
g------------14-----------------14- get the idea D and Dm shapes move them and let your hear guide you.


remeber lifting your fingers (do not let ring the notes) as you are sweping
this is CRITICAL.

e----15p12--------12-12p9-------------9- Malmsteen style
b----------12---12----------11-----11----
g------------12-----------------10--------
in this case use your index finger on 12 fret and lifting it realy smoot like doing a "U" in both direcctions of the sweep its realy hard to do it I still cant get it so I use palmuting all the time.