So there are kits on deadrail installs that have the decoder and a battery. I assume the Bluerail board itself is separate? If I'm installing it in a premier steam with a big can motor, would you recommend the 5 amp? I imagine it will be doing less than 2 most of the time, and there's a big difference in cost between the 5 amp and 2 amp boards.
Also, I'm assuming I need the external antenna, since the tender is die cast.
It it were me, I'd get the 5amp board. Especially a big engine than might be able to pull a lot. See this link to the BlueRail Users Guide. It discussed the 2 amp and 5 amp board and which one might be right for you.
If you have a metal tender, the recommend the external antenna version. You can NOT add the antenna later on to a board w/o an external antenna.
This is from the BR users group for a question about a metal tender. "The design is such that you cannot add a wire and have it function as an antenna. Go ahead and buy the board with the external antenna. You can can keep the antenna tucked in the tender as long as the tender shell is made of plastic (most are) and you will be fine. If the tender shell is metal we recommend that you mount the antenna on the bottom of the tender and connect it through the a hole in the floor of the tender."
You are right, the BR board is sold separately form the kit. That is because Deadrailinstalls sells more than just BR for loco control.
You might want to talk with Pete Steinmetz at Deadrail Installs. His kits have 11.1v batteries. I have an 11.1v (3 Cells) in my 44ton and it is fine. But in my F7's I put in 14.8v (4 cells). It's a bigger train with heavy coach cars. It might be overkill, but I'll always have enough power. Of course, they are more expensive too. Pete won't steer you wrong.