I have my mixing station and RODI controlled by Hydros. I have several sense ports and several drive ports in use. I have 5 solenoids for RODI control and also have a mix pump in the mix tank that is AC controlled. There are 6 float switches in use. I have a DI reservoir, fresh saltwater reservoir and a mix tank. I also have my two AWC pumps and my ATO pump out there also. It all depends on how much automation you are going to have there as to how many of each port you will need. The Start will give you 4 sense ports and 2 drive ports and the 4 AC outputs so you will need to figure out what device you will need to do what you want and then see if there are enough ports of each type needed on the Start.
The Start controller was not around when I first setup my Hydros at my mixing station. I got a X4 to begin with and added 2 X2's and an XS at first. I now have a Kraken, Blenny, Minnow and a Launch at the mixing station. Not all of that is for controlling the RODI though. I have a build thread that has a lot of info on my Hydros setup. I started it at the mixing station and slowly added to it over time. In my main collective I now have 15 controllers. The tank is a 42 gallon hex tank and is 35ft away from the mixing station in my garage. It may give you some ideas on what you need. You may not be wanting to automate the mixing station as much as I did. Here is a link starting at the first Hydros devices on page 4 post #73. Here is the link Hex Tank Build. If you want to navigate there it is on the Reef Central forum and in Tank Journals and builds. The title is Hex Tank Build. I did touch on my previous controller which was a Digital Aquatics Archon before the Hydros.
Are you just refilling one reservoir with it? If so you will need a low level sensor and a high level sensor and at least one solenoid. I refill my DI reservoir and my mix tank with mine. SoI need a low level and a high level sensor for each. I also need an output solenoid for each. I also have a solenoid for a flush valve for the RODI. I don't have a booster pump. I also have a solenoid on the input of my RODI. So mine is quite complex. I also have a fresh salt water reservoir. It also has a low level and a high level sensor. When it goes low and the contents in the mix tank is ready for use the Hydros transfers the contents of the mix tank to the fresh salt water tank and then refills the mix tank from the RODI. To do all of that it would take more than one controller no matter which ones I would use. But most people do not do anything that complex with RODI control.
There is a RODI output type you can use.It has outputs for the solenoid to turn on the water, output for flush valve solenoid and one for a booster pump. It also has input assignments for the low level sensor and high level sensor. If you do not have either the flush valve or the booster pump you can leave those set to none. Here is the setup for my DI reservoir using that output type. I don't use the schedule but if you only want it to run during certain hours you can set a schedule and then when you get a low level dry and it is during the scheduled time it will come on. I don't have anything set for the flush valve or the booster pump here. I have another output setup to turn on a solenoid that allows water to flow into the RODI unit that is also triggered on when either the DI refill or the mix tank refill outputs are on. but if you are just using a single reservoir to refill you would only need this one output. Hydros has solenoids that are powered off of a drive port on the Hydros controllers. I use them for both the output here and the flush valve on my RODI. My RODI has a manual flush valve so I just got the fittings and tapped into the tubing to the the manual valve so I have both if needed. The flush valve and booster pump are optional on this output and are not needed as far as the Hydros for it to work. You may need them for your RODI unit and if so there is outputs within this output type you can setup to power them. Hope this helps. I think this is what you need to use. You will need the two sensors and have them setup as inputs so you can select them in the output when setting it up. You can also setup a maximum on time in the advanced settings once you know how long the normal run time is to refill your reservoir. I have mine set to 5 hours and 30 minutes on the output for the solenoid for the input of my RODI unit.
