In the past when I installed (in-slab) the perimeter would get 6" OC spacing for the first couple feet or passes, then switch to 9" or 12" depending on size of slab. FUTURE RREFERENCE
OK, I will assume a few things and hopefully point out some pros & cons, along the way
1) Supply water temp of 80f (probably a bit low); in-slab can easily be run with 120f water going into floor (looking for a delta T across supply vs return, to reduce stirping and maintain an even heat across all of the slab)
*Use of a thermostatic mixing valve (purely MECHANICAL and only allows you to control the inlet temperature)
*Use of a powered or actuating mixing valve (may allows for out door reset, control of delta T & max temperatures) ->
CAN GET COMPLICATED AND REQUIRE ADDITION ELECTRONICS TO CONTROL2) You say all loops are approximately the same length, GREAT start
Now about the balancing, I would start off with all loops having the same flow (wide open as possible) and allow the system a few days to get up to temperature and see how the shop feels. Big question is do you know which loops feed which areas because it greatly affects the next step. If there are any noticably cold areas, what you can do is slow down some of the other loops that do NOT go to the cold area. Again give a few days between adjustments, as slabs have SLOW reaction times
***My shop is 48'x80' with an office off one end (4k sf), if I start heating early enough building comes up to temperature within a day. However the first year of heating that building we had a fwe hiccups in the system and did not get started until after it had been 40f outside for a week. Took 2 solid days of runing the OWB wide open to get that slab up to temp; but once it gets there, it stays there
(other than some afternoon solar gains)