Hello KTM, try this site for heat exchangers.
They have the least expensive water/water exchangers I've found.
For Pex and Ktec piping and fittings take a look at:
I used a 30 plate exchanger for my domestic hot water, and a 40 plate exchanger for my hot water baseboard heat. These were recommended and sold to me by my local supplier. I would probably use a 50 plate for the house-heat and a 20 plate for the domestic hot water if I were to do it over again. I have a large house [lots of BTU's needed] and don't use a lot of domestic hot water.
The decision on which exchanger to use will depend on how hot the input water will be, 130* or 170* and the flow rate. Are there times when the clothes washer and a shower are used at the same time?? If so go with the bigger exchanger, you will be happier in the long run.
Also don't forget to install a tempering valve in the hot water outlet line from the heater-tank. My tank will often be at 150*+ and anything above 120* can cause a bad burn on our bodies. A tempering valve is about ~$50.
BTW: I did finally use the Laser-temp gun on my Propane fired clothes dryer, the hottest I could find was about 120* on the drum itself, and about 85* on the vent outlet. So a water-to-air exchanger should work to make hot air for your clothes dryer. You will have to be pretty creative with ducting and piping, but it should be worth it in the long run.
Take care, hope this info helps.