You will need a low dose of provin with a cycle like this especially if incorporating decca with testosterone and dbol, you also want run anti estrogen medication something like Arimidex weekly once or twice a week with this cycle, running 3 compounds that will aromatize highly, estrogen can quickly get out of control if you don't try and control it from the jump. Hcg is no a go completely, hcg will raise testosterone and estrogen, you already will be in trouble running test decca and dbol adding hcg would make this a mess and give you unwanted issues, save hcg for post cycle therapy purposes only. I would also add N2Guard into this cycle for organ and liver function/protection.
Need to know how long you are running this cycle for ? I suggest nothing over 12 weeks max and make sure you have everything on hand before you start this cycle, this is nothing to mess around with. Keep in mind you are running 3 compounds that convert easily into estrogen don't take that lightly.