T-8 versus t-12

Also,I think I will have ot put outlets in the ceiling as these lights have a plug built onto them.

Those $10 shop lights come with a cord and plug for a reason. They may not last long and the cord makes them easy to replace.. Actually I have some that are 20 years old, I have also had others crap out in a year. I put 4" boxes in the ceiling with two duplexes and 4 lights plugged into each one.

T8s are significantly brighter than 40W T12s, partly because magnetic ballasts tend to under-run the lamps pretty significantly, and partly because there are advantages to running fluorescent lamps on high frequency that are rather complex in detail, but the result is you get more light per watt, as well as no perceptible flicker.
There is a lot more to it than that too, there are many different phosphor compositions with widely varying characteristics. Most T8s use a trichromatic blend which is much more efficient and has much better color rendering than the old halophosphates. Look at the type number on the tube, it will be something like this:
F32T8/835
Which translates Fluorescent, 32W nominal, Tubular, 8 8ths inch diameter, 80+ CRI, 3500K color temperature.
I recommend 80 series which are 80+ CRI, which compares nicely to the 53 CRI of old fashioned Cool White. The higher the color temperature, the more bluish the light. I personally like 5000K and 6500K daylight best for utility lighting but some prefer the warmer lower temperatures.
You can buy premium T12s with trichromatic phosphors, and you can get electronic T12 ballasts, but it's all a lot more expensive than T8 with no real gain.
Do splurge for some decent fixtures though, the really really cheap ones have lousy ballasts that are low power factor and like to burn up.

It's perfectly acceptable to install outlets in the ceiling, if you look at most of the lighting in warehouses and such they're done like that to enable easy removal of the fixtures for cleaning or replacement, or disconnection in case of a fault.
The $10 fixtures are really cheaply made though, a decent ballast alone costs at least $15. A $25 fixture is 10 times as good as a $10 one.

What about these 15 dollar T-8's? Even though they have a plug, do you think they are ok?
Also, I live out in the country. Because I am doing this myself, I am thinking of using OSB for the walls and ceiling. What do you think? (Painted gloss latex white.)

Hard to say without looking at it. Feel the fixture, does it feel flimsy? Look at the sockets in particular, cheap flaky sockets will haunt you. If the ballast says high power factor, then it likely is at least decent. The electronic ballasts without power factor correction are the cheapest of the cheap, and they tend to not last long. It's not because of their lack of PFC that they fail, but it tends to come with the territory. I've been rather pleased with the Advance Centium instant start T8 ballasts. They're inexpensive, about $15 for the ballast, and have proven to be quite dependable. I've even used them for a lot of things they were never designed to do, like power low pressure sodium lamps, mercury lamps, various fluorescent lamps, even drive small Tesla coils and such and have yet to blow one up by this abuse.
No idea about the walls and ceiling, that's a personal preference, my expertise is in lighting and electronics. If you find you need more light, it can always be added later. Likewise if you end up with too much, you can plug some fixtures into separate switches.