Kind of a stupid question possibly, but I was hoping to find a general maintenance schedule for road bikes. You know, how many miles you should expect out of a pair of tires, how many miles on a chain, crank and cassette, cables etc. There probably isn't a one size fits all chart I would imagine, but maybe some general guidelines? Like how to tell if a tire needs replacing, how to tell a chain is too stretched out, that sort of thing.

If there was one pretty little page that gave all this basic info in one spot, that would be pretty handy. I guess I could search each individual question out on Sheldon Brown's website, but I thought I'd ask here anyways.

What bike do you have?
Where do you ride?
What is your profile as a rider?

Learn to inspect the different components of your bicycle. There is plenty of literature out there to guide you. Such as how to check your chain for stretch, wear on brake pads & rims, tires, etc. There is no magic one-size-fits-all formula. Each bicycle and rider are different. And this varies year by season by month. So do some homework. What's more: It's fun!

Tires vary all over the place from 1500 miles up to 12000 for my PaselaTG 35mm touring tires. For the mechical stuff go to https://www.parktool.com/repair/.
Replace a chain after 1/16" wear (streach) in 1' of length. Remove, clean, replace and lube the chain every 650 miles. Sooner if you spend a lot of time in the rain.
Replace the cassette when a new chain slips on the cogs.
Overhaul your hubs every 2500 to 3000 miles unless you ride a lot in the rain. Then a shorter interval.

Fully inflate the tires before each ride.

That's what I thought you'd all say. But that's ok, because you're all very right.

I guess I'm slightly concerned with the chainring/cassette combo along with the chain mostly because this is a used bike. I have, sadly, only put 436 miles on it so far, but I forget the previous mileage on it. I need to dig up the computer that came on it (passed it on to my inlaws) and figure that out.

It's an '06 Specialized Roubaix. I feel the cassette looks good, but the big chainring right behind the crank arm shows shorter teeth than all the others. I assume it gets a lot of grab in the spot from the force of the pedal when shifting under any sort of load.

I'm also concerned about the tires because they're cheapie bontragers that say "inflate to 100 psi" on the side. I ran 100 psi in the rear and it felt and looked like I was about to get a flat any moment. I probably need to replace those just because....

The big chainring is probably supposed to be like that, unless all the teeth are worn down. On modern chainrings, some teeth are shorter to aid chain shifting.
If your tires do not have cuts or are not cracking, they are probably OK. If you see a lot of cuts or the tires are very thin and cracking, replace them.
For the chain, measure 12" from one link rivet. It should be exactly 12" to the rivet at the 12" point. If it is more, even a fraction more, replace the chain. If the new chain jumps on the cassette, replace the cassette.
Check for play in the bottom bracket by grabbing a crank and trying to move it from side to side perpendicular to the frame.
Check for play in the wheel bearings by holding the rim and moving it gently from side to side.
Check for play in the headset by applying the front brake and pushing the bike to and fro while feeling for play around the bearing cup just above the fork or below the handlebars.
How does the bike feel when you ride it? Are there any unusual noises?
Lubricate the chain once per month; check tire pressure before each ride; check condition of tires before each ride; clean chain when it appears really dirty. This will depend upon your riding conditions.
There's more, but don't become obsessed. Enjoy riding!!

Since it's a used bike and if you don't know it's maintenance history, I'd do a complete overhaul including clean and relube all the bearings and components, lube all of the pivot points,fit new brake pads and new cables and housing. That way you will have a known starting point for future upkeep. Check the chain for elongation as noted above and, if it's within limits, just clean and lube it. Chainrings are very durable and typically last 10 of thousands of miles so it's unlikely they need to be replaced.

Any tire that's really at 100 psi shouldn't look "flat" so check to see if your pump gauge is reading properly.

If the big fat Texan is true try 28mm tires. I think you have clearance on that bike for them. Be prepared for spoke breakage problems. Heavy riders need 36 spoke wheels for reliability.

Wow,,,that's some mileage!

Nah, I'm not that fat, but calling myself fat helps keep me on the bike. I'm about 210 right now (6'2").

I have long suspected my gauge might be out of whack. I need to go pick up a Park tools pump sometime soon.