@Djsleepy it sounds like you'll be better off getting more cooling units and stems than worrying about the screens. I have 2 cooling units and 3 stems (4th coming this week - wanted to try the grav upline taster). Sometimes I wish I had a 3rd cooling unit and my usage doesn't seem to be as frequent as yours.
I wouldn't go any less than 2 CU's. For me what I usually do is pop out a dirty cooling unit, put CU/stem in ISO, and put in a fresh CU and stem. Usually let the dirty one sit over night. rinse in the morning, dry and set aside. 5-7 days or so, repeat. I generally pop them out when I can see some resin creep in between the CU wall and glass stem... I could probably go longer. Typically 1-3 stems a day. So far, I haven't noticed the *optional* basket screen in front of the CU doing too much for keeping the CU clean when it comes to the resin. Yes, it does keep large debris from getting on the CU but even with out a basket screen, thats easy enough to pick off with a toothpick. BTW the CU has its own screen, so think of the basket screen as a double layer screen between the flower and cooling unit.
Occasionally when I was too lazy to clean the first dirty stem, thats when I wish I had a 3rd CU lol. But really for me 2 is totally fine.
Also something to keep in mind, it seems like the CU's are mostly (if not strictly) for the stock stems. So for a stem like the Grav upline taster, you wouldnt use a CU.