As for the shredding, I can't remember "starting out". All I've done is to play every solo, every piece of melody, every scale I ever learned, indeed, every piece of music I've ever played to a metronome, and speed has simply been coming gradually over time.
What you can do is set the metronome, to a relatively slow setting, perhaps around 50-60 bpm, then start out with 1 note/beat, then 2 notes/beat, then 3 notes/beat, 4/beat, 6/beat and finally 8 notes/beat.
If you feel you're pushing yourself at 8 notes/beat, then lower the tempo about 6-8 beats at a time. If it's slow enough not to be a challenge at all, then increase the tempo!
The important thing here is that you should NOT play just one specific pattern using this exercise, or you'll end up having your fingers used to only this pattern, and as soon as you're gonna play something that uses another pattern, your fingers won't want to. Stick to one pattern for perhaps 5-10 minutes, and then try another one. The different scales + the chromatic scale are decent patterns, or you can figure out various patterns yourself by looking at which finger movements you need to practice most.
Sorry if it's a bit muddy, ask if there's something unclear.
As for the sweeping, I did what you do yourself, and I don't really know if there's much more tips on that one... apart from using a metronome there too.
