My experience is definitely not with small breweries. However, assuming you are running at 50 bpm consistently and the bottles are .5 litres, then flow rate through the filler is only 15 hl / hr. I have my doubts that anyone will make a flash pasteuriser this small, certainly with decent temperature and flow control. The cost of a decent pasteuriser unit, assuming you can get one will be horrifically more expensive than sterile filtration.
I suggest you stick with sterile filtration, so you will need to prefilter with KG, then to extend the life of the sterilising filter (0.45 micron absolute) you will want a 5 or possibly 1 micron trap before hand. You will probably only need about 4 x 10 inch cartridges for each filter cartridge housing, but check with a supplier such as Parker, Sartorious or Pall for exact details. You will need to allow for backflushing and steam sterilisation for hygiene and extended working life, but even so your costs should be far less than a flash pasteuriser