I have a HG/BM setup that works well, but I'm not getting the coffee I think I should.

My HG is an adjustable porter cable.

Do you think it's better to drop high and reduce temp, start low and increase temp, or try to keep the temp input steady?

Also What time do you try to hit first crack? Do you then follow Rao's 75-80% "rule"?

You're flying blind till you get a temp probe mod on your roaster. Just order a k type thermocouple with display, a long rigid one works well, and once you have it, drill through your shell and bowl to put the probe out of the way of the paddle but near the bottom for a good bean temp readout. Easiest to drill the bowl first, actually.

There are so many variables in this style roaster (aka the Coretto roaster), that there is very little standard about them. I found I could roast about 300 gms with FC start @ 7-9 mins, and get very good results. My coffee got better when I stopped trying to overload the roaster. I also used a variac to control my heat gun, because the changes required are subtle, and it was easier to manage than with steps. Starting higher and decreasing power was wher I found the most success. And yes, I used a chart that conforms to Rao's finish times from FCs, to help me determine anticipated finish.

Everything Steve said, plus get Scott Rao's book, "The Coffee Roaster's Companion." It's not a roasting bible, and not all opf it will be useful, but it will give you an excellent understanding as well as a sound foundation on which to build.

I have a thermoprobe, roasting software, and Rao's roasting book.

When I used a HG/BM, my standard protocol was to pre-heat the roaster body to around 325F, start the roast a bit slow, progressively increase the heat gun power throughout until it hit around 525F MET. At the start of FC, I would start tapering the heat back down, with the speed of the taper depending on how long of a development time I liked. I highly recommend figuring out a way to get continuous rather than stepped control of your heat gun, whether with a variac, a dimmer switch, or just choosing a heat gun with that capability, as that makes it easier to get control over your profiles.

In addition to Rao's book I also recommend Rob Hoos, Modulating the Flavor Profile of Coffee.