> How did yall get over being nervous?
You don't. :)
The evening after I closed on my first (and only, so far) rental property, I would randomly exclaim, "Oh sh(oo)t, I bought a house!", until my other half was tired of hearing it. :D The next day, I piled my tools in my car and drove over there to start rehabbing it.
A few random, specific tips:
Depending on how good the lawn care / other tenants are, the outside of the house may look OK, or not so good. If it looks not so good, consider doing what you can to clean it up, right after you take possession. I bought my house in February and the yard was full of sticks, there were leaves from last fall against the front of the house, and so on. The second or third day I owned it, I cleaned all of that stuff up, just so it would look better in the neighborhood. I was trying to show the neighbors that I cared about the property.
Once you get the roof replaced, make sure your insurance knows about it. They may be able to reduce your rate a little.
If the units currently have bathroom fans and kitchen vent hoods that exhaust to the outside, good. If not, consider adding them - or at least the vents for them - while the roof is being done. It will take the roofers maybe an extra hour of time and $150 in parts to do now, and you will know that the new shingles are sealed correctly around the new vents. If you call a roofer out to add them later, you'll pay a few hundred dollars, plus they'll be banging around on the roof again - doing it all at once means the noise only lasts for a day or so. If you don't install the fans/hoods immediately, ask the roofer to put a cap over the inside of the vents when they are installed, to keep birds, bugs, bats, etc out of the attic. When the fans/hoods are installed later, you will remove that cap, throw it away, and connect the ductwork where the cap was.
If the bathroom has a window, then by most building codes, it doesn't have to have a fan - the idea is the people will open the window when they run the shower, but nobody does that. If there is a fan installed and working, most people will use it, especially in the summer. This helps keep mold and mildew out of the bathrooms.
The recirculating kitchen vent hoods do work, but not as well as the ones that exhaust to the outside. If you or your tenants cook a lot, they will probably appreciate the outside exhaust, because it keeps grease, steam, etc out of the kitchen.
Go in to the empty units and see what you have. Take photos and make notes on things you want to fix / upgrade / change. The PM "should" check the units immediately after the tenants move out, but it's also good to check yourself, to make sure they didn't leave food in the fridge and then unplug the fridge, or leave a faucet running, or whatever.
If you can, try to fix things like carpet/flooring and paint in the unit you will live in, before you move in. These are a lot easier to do when the unit is vacant. Minor plumbing and electrical things (new faucets, new outlets and switches) you can usually do after you move in.
12-year-old HVAC is not too big of a deal, in my opinion. If the PM doesn't already take care of it, you might think about scheduling a service call on the two vacant units, just to make sure they are in good shape before you or the new tenants move in. You can change the filters and vacuum out the blower compartment in the furnace yourself, and you might think about hosing out the outdoor units - but if you're not comfortable doing that, ask the HVAC tech to check the outdoor units.
Good luck!