I'm not sure what you mean by "outtake". Do you mean the pump discharge or the tank outlet?
The simplest method of adding concentrate is to simply add it to the water tank. The problem becomes mixing it evenly, so you have to use more concentrate to ensure a minimum concentration at all times, which is wasteful. Plus it can be an issue with some pumps.
A refinement of that approach is to meter the concentrate at the pump inlet, using gravity or a venturi to draw the correct proportion of concentrate. This is less wasteful and limits the concentration going through the pump. Principle drawback is that the concentration will only be correct at a specific flow rate -- your photos look like you have 2 discharge outlets, so your foam concentration would be almost halved if both are in operation compared to just one. You would have to use a valve in the concentrate line and do some experimenting to find the right setting for the correct proportion.
The most common method in use by fire departments is via eductor at the pump outlet, but I don't think that will work with your pump. From what I can see, you have ABS piping and polycarb nozzle, making me suspect your discharge pressure is limited to around 50 or 60psi. An eductor typically requires 200 psi pump pressure. Plus you need a separate eductor for each hose outlet.
If you put a slightly different eductor between the pump discharge and the pump inlet, you get an around-the-pump proportioner. It can feed more than one hoseline, but still needs 100psi or so pump pressure.
A balanced pressure proportioning system uses a bladder tank or separate foam concentrate pump to inject concentrate into the pump discharge. It accommodates a wide range of pressures and flow rates, doesn't put any concentrate through the pump -- but it ain't cheap.
The ultimate system would be a slide-in standalone CAFS unit. Designed to fit in a pick-up bed like a tool box, they incorporate the water pump, foam injection system and an air compressor to make the perfect foam first time, every time with concentrations as low as 0.1%. But as with everything aimed at fire department use, you could probably buy a new tractor for less.
Once you have decided on how you are going to get the concentrate into the water, you next have to decide on how you are going to generate your foam. That will depend on how much pressure you can supply to the end of the hose and the volume you can deliver at that pressure. A simple fog nozzle like the one in your picture is going to produce a very wet low expansion foam.
It would be nice if you can get a medium expansion aspirating nozzle and get up into 20:1 or better. If I'm correct in my thinking about the volume and pressure you can expect from that pump, then something like the Task Force Tips FJ-MX-060 (60usgpm@60psi) or even the FJ-MX-080 (80usgpm@60psi) might work.