Server Automation

Hi, I was wondering if someone could point me in the right direction as I am looking to reconfigure my current (hobbled) setup.

My current setup is:

ISP Speed: 150/Mbps

Usenet Provider: Newsgroup ninja

Programs: Sabnzb, Sonarr, Couchpotato on windows 7 laptop (that I am getting rid of soon. Its old and Junky)

Indexers: nzb.su, nzbcat, simplynzb

I manually transfer the completed files via smb share with my latptop to a Pi2 Plex Media Server with a 2TB ext HDD.

What I was thinking was setting up Sabnzb, Sonarr and Couchpotato on a Pi3. However I've read that processing/ unraring is slow. Would I be able to get my iPad to handle the processing of Sabnzb?

I guess what I am wondering is what would be the best server that is low power and can run 24/7 for sab/sonarr/couchpotato?

Thanks!