A fan works very well. One adjusted to the nominal height of the plants works even better. ETA- I'd run it for a few hours every day, and even longer when it's warm (60F +).

I switched to running DC brushless fans and they are awesome. Save a lot of money on electricity and they should last much longer too. Two of mine are something like this: https://www.vornado.com/shop/circulators-fans/533dc-energy-smart-small-air-circulator

I use a few different fans. For the plants under lights, I use a small fan that is very quiet and circulates air over the eight feet I require. They are on the same light timers and only run when lights are on.

In the greenhouse, I use a larger Honeywell TurboForce HT 900. During the winter, it hangs just behind the heater to circulate the heat and runs 24/7. It’s three years old and runs quietly and has enough air flow be felt throughout the greenhouse. Honeywell Fan

To supplement airflow higher up in the greenhouse, I use generic clip-on fans which also run 24/7. This is not a DC fan but for about $15.00 online or Walmart, it’s a great value Koi

What I see looks great, but what do I do? Take a look at what I am doing, one fan 10' from the shelf hitting all the levels. But its a pain due to being just in the door.

Can I put small fans at each level? I would thing low rpm models. Or do I stay this way only closer to the rack, which fan could do that job?

I think all are good options. On my three-tier shelf I just blow across the middle shelf. It's open enough everything gets good airflow. On my counter it is a longer setup like Howard's and I blow lengthwise across all my trays.

The Honeywell worked for me but eventually burnt out. Many fans I had lasted around 3 years but hopefully I can get 5+ with my newest ones.