Unless you dug a 2-3' deep trench across the root area, I really don't think it will be a problem. The volume of the 4-8 post holes you dug really, as Ken said, is very little, comparatively speaking, with the greater root mass. I would also agree that mulching is always a good idea (as widely as possible, no deeper than 4", and no mulch in the 2-4" next to the trunk), and a really, slow, deep watering won't hurt either, unless you just GOT 4" of rain in the past week. If you did, I am very envious - we've had 4" in the last 4-6 months!

We took down a huge red oak last year, both my wife I cried the day they came with the chainsaws. The tree had a fungal infection, which was confirmed by sending the fruiting bodies, those "mushrooms" that were growing around the base of the tree, to a lab for analysis. Usually, a fungal attack kills a tree from the inside out and can take years and years to occur. What you have to remember is that trees distribute water and food through their outermost layers of trunk, the phloem and xylum. What that means is that a tree can look perfectly fine on the outside, while the inside is all but gone. And this makes for a dangerous situation. It's what arborists call a "hazard tree." A word of caution - be careful about whatever "tree man" you use. Some are very knowledgable, while others are just guys with a chainsaw and a truck. We had several certified arborists examine our tree, and what we found was that fixing it was very expensive, and came with no guarantee. We were told that if this tree fell on our house, it would destroy the attic and pretty much all of the second floor. Not a very comforting thought. They all seemed to favor taking it down to be 100% safe, and so we did. Sorry to lay out what might be too much info here, but we went through the process over the last couple years, this was after what was deemed a healthy white ash blew down in a thunderstorm and destroyed a brand new vehicle. Please understand that we are big tree lovers. However, we have also come to realize that some trees, meaning big trees with problems, are very, very dangerous. The link attached might be of help. One final thought. It's often said that a little knowledge can be a dangerous thing, and I've come to believe that. I took an arborculture course a few years ago, and that's when I started looking at trees, all trees, with an element of respect and fear. Good luck, please let us hear what happens. Here is a link that might be useful: Hazard Trees

Oak trees, at least the kind I'm familiar with in zone 6A, are superb for having shade gardens under them. Their roots are deep and don't inhibit the growth of shade plants. So, it a shade garden is what you want, you can plant right up to the trunk.

"it's just not done" I think the pic you've already posted here would be of more concern to most people than a closeup of the tree canopy! Not completely discounting the lightning theory...but my guess would be if a tree this close to houses was struck, it would have been a quite notable event for at least all of the immediately adjacent houses. I think glass panes can be broken by the noise at that range, and the electrical surge via ground can damage appliances. And at least throwing a branch or two down from the canopy or in some other way memorializing itself. But looking at the picture it does appear the damage radiates from a single path coming down from the top of the canopy. Maybe it was a smaller strike that was a finger of a bigger one?