Hey Danielle,
Something I check every time when I'm on a walkthrough is the age on the water heater and AC Unit. You can usually find it on a sticker on each appliance. If it does specifically say "MFG Date", with most brands it is the 3rd/4th digit of the serial number. (ex. XX20XXXXX would be 2020). The other is the roof - In Florida there is a line on the Seller's Disclosure that usually says how old the roof is, but I also like to use my drone. I'm an agent and use it for work so I have a Part 107, but I'm not sure if you would need one for this. The general rule of thumb is that if you make money using it, you need a part 107, BUT since you're not really selling the footage for money... It's a grey area. If you plan on buying a lot of investment properties, I think it is worth the investment. It's a game changer when you can pop that up and in 5 minutes get a good idea of the condition of the roof regardless of the actual age.
Since these three things are some of the most obvious capital expenditures you could be facing, it's always a good idea to get their age written down. I know a 4 year unit can shut down and stop out of nowhere and I've seen 20 year units still chugging along, but it's still good to have an idea for it.
Another thing I like to keep front of mind is bathroom space. If you're looking at a 4/2, but one of those is the Primary Bedroom with exclusive access then you're looking at 3 of your room sharing a single bathroom. Which is doable, but then if you plan to take a room and make it a 5th... You're starting to get an unrealistic number of bodies going through one bathroom. Especially if you're going to be house hacking.