Tom, You are correct on the "temperature". Daylight is generally 5000K. The LEDs I got from Costco were 4100K and they are acceptable. I wouldn't go any lower. As to brightness, lumens, you should be able to find a spec for the bulbs you currently have and compare it to the LEDs you intend to buy. Is your current lighting adequate? If not, don't worry about the lumen output of the LEDs. It probably is greater than what you have. I find lumen specs for these bulbs to be a little misleading. I just replaced 4 CFL 40 Watt equivalent (We) bulbs with 40 We LEDs. The specs were about a 10% increase in lumens but the room is substantially brighter, a whole lot more than 10%, with the LEDs.
If you're concerned with overkill, you could try to install 2/3 the number, but leave room for a 1:1 swap. Unless your shop was already very bright, you'll probably like a full swap to LEDs. More important, though, is to consider the placements so that you get the light where it is most needed.
Are your current lights chained together. If so, no problem since LEDs draw about 20% less power than fluorescants. If not, add up the wattage of the LEDs. While you can put about 1500 W on a 15 amp 110V circuit (if there's nothing else on that circuit), I wouldn't go over 1200. Unlike Christmas tree light strings, I don't think they spec a number of fixtures that can be chained.
The best deals on these lights used to be Costco; 2 2-bulb 4' fixtures for under $50, but they seemed to be in batches. They'd have them for a few weeks, then none for a couple of months. Ocean State Job Lot had two varieties of 2-bulb, 4' fixtures recently for $17-18 each. Don't know if they still have them. I'm told that the Habitat for Humanity Restores sometimes have them for a similar price.
