1. How to use nails? I've seen a player pin objects to walls and floors somewhere.
2. Does the amount of light turned on affect the cycles of the generators? To paraphrase: Does the amount of light turned on at the base affect how often the generator will fail?
3. Why increase the levels of recordings (cassettes)? Do they increase the cost or is there another reason?

Well, I am unfamiliar with nails, but as for the other two questions, turning off stuff should preserve some power, but the generators can last a good few days. Though, it couldn't hurt to buy more stability when you can. For the signals, upgrading them does reward you more, and allows you to hear the signals as they are supposed to be. Less static and actual sound. Upgrading them all the way to level 3 will net you the most profit and the intended experience of the signals.

To use nails you need to buy a 'Hammer [WIP]' from store, and click LMB while holding a hammer to place a nail (you need to have at least 1 nail in your inventory)

I don't know if amount of light turned on affects the transformers, but it probably is, i've seen several videos of other people playing the game and I think people who turned off the lights needed to fix the transformers less frequently, but it may be just a coincidence

Increasing the level of drives increases their cost:

Most signals cost 5 for level 0, 10 for level 1, 15 for level 2 and 30 for level 3

"Garbage" (noise) signals cost 20 for level 3 and same for levels 0, 1 and 2

Some of event signals cost 30 for all levels

Some rare signals cost 0 for level 3 but same for levels 0, 1 and 2

Repeating event signals (these mostly have small size around 0.25 MB) cost 0 for all levels