You really should do a heat loss analysis (e.g., ACCA Manual J or equivalent) of the building that you be will heating with this HR system. Then you can properly determine the HR system supply temp and flow rates that are needed to accomplish this mission at the outdoor design temp for your location. One can’t really spec a pump until the flow rates and PEX circuit lengths have been determined. Nevertheless, I suspect your Taco 007 pump will likely be okay for three 300’ circuits. We have some free software on our website that would allow you to accomplish all this DIY if you are so inclined:
Borst Heat Loss Analysis Software
Borst Hydronic Radiant Floor Heating Design Software
If your PEX is toward the bottom of the slab with rebar above it, you are at much less risk of encountering control joint damage to the PEX during the actual cutting or subsequently when the concrete actually cracks/separates at the control joint locations and pulls/stretches the PEX. Nevertheless, it is still good practice to sleeve the PEX where a control joint passes perpendicular to the PEX. You can use a larger diameter section of 12” long PEX that is cut longitudinally to facilitate snapping over and protecting the operational PEX. This gives the operational PEX a 12" distance to freely stretch which can be safely accommodated by the PEX versus something much less if it were not sleeved.