Can I taper off of a (relatively mild) heroin addiction? Why do people use suboxone and methadone?

I have been insufflating tar (I know) for two months now and need to cut it out. It seems like I'm not in too deep, but I am way further in than I planned and I so so so want to cut it out. I use about 300 mg a day of pretty good (SR) dope.

Other stories indicate that's enough to expect withdrawal. I still have a reasonable stash (2.5 g) and was hoping, with a plan tapering down over twelve days, I could avoid W/D. Is this true, or realistic?

I was thinking starting w/ 5x50mg for 2 days, going to 5x40mg for 2 days, then 2x30mg and 3x40mg for 2 days, then 4x30mg for two days, finally 3x30mg for two days, at which point my total will be @90mg/day and, I hope, I can just quit (go to 0) and be OK?

Why do heroin users usually switch to suboxone or methadone to detox? I'm hoping it has to do with the rush and that by not IVing I have dodged a bullet.

When MDs take someone off, say OxyContin, after treating pain from an injury for a few months, they do a taper something like this, no/yes?

Also, any advice on how to deal with the mental side of this? I know even if that schedule works physically, there's gonna be times I really want more just because I feel sad/bored/crap-things happen and I haven't had to deal with that in awhile now...

(Edited the numbers because they got mangled.) (Not because of why you think.)

Update 5/3: It worked! A few failures of will strung this out to 19 days, instead of 10, but I'm clean :D with basically no perceivable sickness along the way. My thoughts & support go out to the many who want out of deeper holes than my little rut. And thanks to everyone who responded with advice or support.