How bad is it if my temp gauge is sitting right at the line before red?

Seeing the temperature needle hit that critical zone means the cooling system is seriously struggling. That low reservoir reading you found is the most obvious and most likely cause of the immediate spike. When the coolant level is significantly below the minimum line, the system loses its ability to transfer heat effectively, causing temperatures to climb rapidly. But if the level had been fine, then you could be right and it could be a failure of the thermostat or the water pump, either of wich is common on these models. Given what you found, I'd bet on the low volume being the culprit.

Before you consider driving it anywhere else, you have to ensure the system is actually filled to the correct level, not just topped off. Just because it looks full doesn't mean the thermostat or the cap isn't faulty. After you add the coolant, let the car sit for a while and watch the temperature gauge closely. The ideal scenario is that after it warms up and the needle climbs, it settles and doesn't start creeping back toward the red zone. If it immediately starts climbing again after being full, then you definately have a mechanical issue that needs a mechanic. If topping it off and letting it stabilize resolves the heat issue, then you're likely fine for the immediate trip, but you need to address why the reservoir was so low in the first place. Low coolant levels ussually point to a leak somewhere—it could be a hose, the radiator itself, or a drain plug. Don't just assume it was a minor evaporation issue since you just finished a long drive. A leak under the hood is a serious maintenace concern.

Regarding waiting before a long drive, if the engine temperature remains stable and within the green zone after the top-off, you should be good. Just keep an eye on the pressure cap to ensure it seals correctly. I've seen cases where the cap fails and the system pressure drops, leading to rapid boiling even when the coolant looks okay. Keep that in mind before pushing it further.

Same thing happened on my wife's Escape a while back. Topped it off, gauge stayed normal for a week, then it was low again. Turned out to be a slow seep at the lower radiator hose clamp, just enough to leave a crusty pink stain but never a puddle. I'd put some cardboard under the front end overnight and check it in the morning before spending money on anything.

Also only check and fill that reservoir when the engine's cold. Those plastic tanks on the 2.5 engines get brittle with age anyway, so don't crank the cap open hot.

That thing about the pink crusty stain is helpful, I'm gonna look for that tomorrow. My old Civic used to run warm and the giveaway for me was the heater blowing lukewair instead of hot, aparently that's one of the first signs the liquid level is down. I never would've connected those two things untill a buddy told me. Does the Escape's heater also go weak when it's low like that, or is that a diferent setup? Also when you guys check the bottle in the morning, do you look at it cold or after running the engine a bit? I've heard both matter.

I'd push back on the part where a stable gauge after a top-off means you're good for a long drive. On these Escapes the gauge can sit normal for days while the level keeps dropping, so a calm needle tells you very little. My brother's 1.6 never once ran hot, it just quietly drank coolant for months before the leak showed up anywhere visible. If I were the OP I wouldn't trust one warm-up cycle as proof of anything, expecially with how much these engines are known for losing coolant somewhere you can't see. Pressure test first, road trip second.

Been fixing Fords since before these things had computers in them, and one old trick still works. With the engine cold, squeeze the upper radiator hose. It should feel firm-ish, not squishy like an old garden hose. Then have someone start it while you hold the hose and feel for coolant rushing thru when the thermostat opens. If that hose never gets firm or hot, the thermostat is stuck or the level is too low to circulate. Also crack that reservoir cap cold and sniff. A sweet smell with white crust around the cap means it's been venting pressure, and a worn cap on these is cheap enugh to just replace on principle.

Update: took the tip about putting cardboard under the front end overnight and sure enough, faint pink spots showed up by morning near the upper hose area. Clamp had loosened up. Snugged it down, refilled with the proper mix, and the level has stayed put for two weeks now. Also keeping an eye on it anyway since someone pointed out the gauge can look fine while coolant still sneaks out.