I setup acarsd first. It's been busy today. Might try KG-ACARS also when I have a chance. Don't want to tie up the RTL-SDR dongle but there's enough traffic to dedicate it for acars. Probably I'll get a couple more for my main interests of SDRSharp, SDR-Radio and DSDPlus.
No problem, you'll be overwhelmed with data in that area! There will certainly be multiple frequencies in use with R-C ARINC. I've never read any evidence of SITACOM having more than 136.850 in North America. Perhaps you can confirm or dispel that for me as you get going. Here in Canada, that is their only licensed frequency coast to coast. (Not including VDL2 on 136.975 globally, which is a different flavor of "ACARS")
For software, I have ACARSD, Airnav ACARS, KG-ACARS and MultiPSK. Although the trickiest to get set up, MultiPSK formats the messages more accurately (recognizing the proper message types and fields) than any of them, with ACARSD a close second.