I've only seen coolant in the oil once. Very blown headgaskets. Not the early initial stages when the coolant just keeps disappearing, or small bubbles in the recovery tank. I've been down this road a number of times.
My experience with the coolant level you describe - it may have been drawn down by a slow leak anywhere - to the outside of the block, down the intake. But the level low in the radiator + over normal temperature [does not have to get into or even near the red] has always lead to failed head gaskets, it might be 6 days, might be 6 months. I never had one consuming coolant down the intake at a high enough rate to show smoke [steam] in the exhaust.
To have a chance of saving it while troubleshooting, checking the coolant level before every drive is the only way. Do not open the radiator cap, check the bottle level. check the radiator by sharply squeezing the upper hose, and listen for gurgles and the jiggle pin. A tiny amount of air is ok, but a really tight system will have none. The important clue is does the amount of air increase each time you check? Does the level in the tank constantly get lower every time? When the leak is in the beginning stages, it will be very slow, takes a week of doing this to start to get an idea.
I also found that running a zero pressure cap helps sort out whether this is air leaking in vs head gasket beginning to inject exhaust gas failure.
At high altitude, it might not be a good idea to run zero pressure, but where I am, I never had a problem.
When it's an intake or external leak, a pressurized system will force coolant out while hot. While cooling, air sucks back in through the leak.
When it's a combustion chamber to coolant leak, the explosions force exhaust gas into the coolant long before coolant can leak into the cylinder. Think about the difference in the pressure involved on either side of the gasket...
With zero pressure, there isn't suction while the engine cools, and you loose less while running, because it isn't being forced out. If it's an intake leak, the vacuum will still pull it out, but without the help of the 13PSI pushing it also.
You could try just doing the throttle body and intake to head gaskets, but it would be good to do all the above monitoring first, to determine if the exhaust gasses are getting into the coolant, because that only means one thing.
Regardless of how far you have to go - removing any of the engine bolts is best done with the engine [the mass of aluminum, not just heating the bolt head is the key] near 180degrees F. Unless you have previously disassembled it and used anti seize compound. I have been amazed at some of the bolts that I got out in one piece using this trick - they would have certainly twisted off if done at room temperature. The worse ones still took carefully rocking them to work them out, but none stripped or broke.