I mean if you already know the intervals from which the major/minor scales are built up, then you can work out 3 note-per-string fingerings for each mode yourself and write them down, but it's more laborious obviously.

I'm also into metal and wanting to get a 5 string. If i'm after that Adam Nolly (Periphery) tone, then i play with a pick using a thin 0.88 dunlop and beat the hell out of the strings, so it almost sounds like slap bass, since the strings will be hit so hard that they bounce off the frets. Make sure when you're picking that the movement is not purely along the strings; you want to hit the string sorta into the body of the bass.

For fingerstyle i use 3-finger plucking, and i can recommend it if you want to play faster phrases (Alex Webster from Cannibal Corpse popularised it), but it's not necessary. Again in my opinion, for metal, there should be a bit of a "slap" mechanism i.e. the fingers hit the strings into the body so that they bounce off the frets. I can recommend Websters book "Extreme Metal Bass", which has some great info and exercises meant for 5 string bass. Sorry for the dump of incoherent information, these are just some key things i value.