Listen to be perfectly real with you, having tried all of the above that you've named, I wouldn't recommend trying to "build up" to heroin. It's just not that kind of drug man. It's not a drug you pick up and put down. It's not a weekend drug, a "sometimes" drug. If it were a party or occasional drug like that, there wouldn't be so many opiate addicts out there with shattered lives. There is a reason people choose heroin over their jobs, friends, families, houses, children, etc. It is just different man.

However in the name of harm reduction, I will answer your question since you're gonna do what you're gonna do. Yes, id recommend building up. You likely won't have a good time doing H with no tolerance. Kratom is nice especially with no tolerance. I would stretch it out and get by using krat/oxy/hydro for as long as possible before the H if you really insist on trying it. No reason to rush it IMO. Heroin will always be there.