Attack speed might benefit you, having 2.2+ aps is really nice for multiple reasons including hatred gen, sentry firing rate, and bola spray stacking. You could swap boar for Guardian turrets and get a straight up 15% DR for hatred to conserve your Disc for vault/Gloom and have a nice supplemental damage source as well as far more defense. With my passive setup including numbing traps my spike traps, sentry fire, and caltrops give 20% reduced damage + the 15% from being in turret bubble and another 35% for glooming. You can use the Bait the Trap caltrops for an instant +10% crit and also 20% DR to anything within range as well as a way to slow enemies to retreat (Fallen Maniacs), I spam this constantly as it gives me 23k dps boost and is very cheap on discipline.
This is of course basically using my setup which is a very different play style that doesn't suit everyone, I like all my skills to work well together and offer more than 1 benefit to myself and whoever I'm playing with.
As far as gearing figure out your limitations, mainly legacy nat's. They are ilvl61 so 60res is max, you can get over 200 vit on a shadow though and 170 dex on boots. The helm with crit is nice but with good enough jewelry/gloves you can go for Allres / Socket and throw an 18% lifer in there. If you want at least +10 max disc you gotta sacrifice stats somewhere, I'd go for the cloak since DML can roll 300+ dex 300+ vit that will offer a far better bonus than the extra 125ish vit on a double rolled shadow.
Well Life steal is amazing to have base on your weapon and is 100% more effective than life on hit, I rarely gloom unless i'm tanking multiple affixes at once or just out of habit. Not a huge fan of the Pets except bat, they just don't do much for you. I run 30 max disc and never have an issue whatsoever in my build, 40 is insane and 48 is something I'd expect to see on a non legacy build. Keep in mind you can swap gems to suit your stats, so if you have vit gems in something and get vit on your bow you can switch them to dex.
Unfortunately you get to a point which you are kind of at where significant upgrades cost 500mil or more, and end game gear is in the 1-2bil+ range. Either way looks pretty solid as is so be patient and look for GG deals
Oh, the pet + max disc is to increase farming efficiency. I wanted as much max disc as I can get because I am obviously behind on plvls.
I have a 56 res nats cloak that I plan to use once pvp rolls over but all other upgrades, as you said, are going to cost upwards of 100 mil :(.