There is indirect PvP aspects in Planetary Interaction, and soon there will be direct PvP aspects with the release of a console game called DUST514.
The indirect PvP aspect is fighting over resources. This was only turned on in some of the later patches in the Incursion. On each planet there is only a limited number of the resources in the ground, which only refill at a certain static rate. The planet will support some (unspecified) minimum amount of resource being extracted, then after that it will deteriorate. This means that too much concentration in the area will deplete the resource for all players pulling that resource out of the ground at that place.
The direct PvP will come later when the DUST514 console shooter game comes out. Exact details haven't been confirmed yet, but the base premise of it is that people playing Eve Online will be able to somehow ask players in DUST514 to somehow disrupt other Eve Online players Planetary Interaction networks.
There are usually two types of Planetary Interaction (PI) setups : Extraction and Factory setups.
With Extraction setups, PI doesn't really require any sort of ongoing ISK costs to run besides export fees of planetary products, therefore all PI here should be "profitable". In High-Sec you won't get very high extraction rates at all, and they will be highly contested, which means not very profitable on a "ISK-per-time-invested" basis. Lo-Sec can be better, but Null-Sec and Wormhole planets can be quite lucrative. There is a larger risk in transporting the PI products from these lower security areas of space though.
With Factory Setups, people can make a fair amount of ISK by making PI setups in High Sec that purely concentrate on turning lower level cheaper PI products bought from the market into higher level more expensive products. You'd need to figure out what is profitable here and what isn't as it would also be quite easy to lose a lot of money doing this if you chose the wrong products, or the sell prices of the high-end product dropped unexpectedly.
In terms of investment of training time, it doesn't take too long to get decent PI skills. Anywhere between a few days for some basic skills to a couple of months to be able to run multiple planets with high level command centres depending on how much PI you want to be involved in.
I've found that there's a significant difference between the value entered for "orbit at" and the actual average range from the target. And this is for static, non-moving targets! A moving target is obviously going to be even harder to maintain a specific distance from.
What I've found is that I have to start with a 'rock' (an unmoving target about the size I want to be able to orbit at a certain range) and have it selected so that I'm monitoring my actual distance from it. Then start entering "orbit at" values and see how well it works. Keep lowering the value until I'm consistently inside my max range. The value I end up at is typically around 3/4 of the max, but this will change for every ship and even for different fits on that ship; as the speed and agility of my ship change, so does the 'orbit at' value I need to use.
This gives me a maximum 'orbit at' distance for a rock, I can now adjust that further downwards to account for a target that is actively trying to get out of my range. Again, experimentation is the only way to find a value that will consistently work.
Imprecise? Yes. But the game seems to have serious issues actually maintaining a constant orbit distance, so you have to find a way to work with the games weaknesses.
Best Answer
Overloading ( or overheating ) gives a small boost to the module. I'm going to link a couple of resources at the end, because they will cover all of the aspects far better than I ever could. I will, however, give a short rambling on when and why I overload:
Overloading gives a different bonus based on which type of module you are overloading. It 'improves' the function of the module by a specific amount, increasing the effect. The drawback is that the modules heat up, dealing an amount of damage per cycle. If the amount of damage absorbed by the module goes over it's health ( iirc, 40 for pretty much every mod in the game ) the module 'breaks' and becomes unusable until it is repaired.
This is mostly done in PvP, but can see some use in PvE as well. When overloading kicks in, the small boost that is given to the module can be enough to give that extra edge over an opponent - often enough to survive the fight.
The EVE University wiki ( quite possibly the best resource for EVE-O ever ) has a page on overheating, and even a class called Overheating 101 ( and an accompanied recording ).