I did an engine swap ('03 engine into an '02 TB) and I can say that you will have to have your A/C system emptied and disconnect your hoses since you have to remove that top line and the condenser. No way around it.
That is a very good question on the oil pan. I don't think you can because the flywheel might not let you pull the engine forward if the pan is still in the vehicle. And given that some of the tranny bellhousing bolts are on the oil pan will present another challenge as well as the oil pump pick-up that may get damaged during the removal or re-install. It's better to just bite the bullet and remove the front axles.
For the oil level sensor if you use a newer engine and PCM, it won't work anymore unless you hook up your own idiot light to it since no PCM from 03 and up will be able to use it. When I swapped mine, I kept the '02 oil pan and PCM so I was able to keep it functional.
Here are some tips: drop the engine as low as it will go by removing the motor and tranny mounts to be able get at the top bellhousing bolts. Pull the engine with the differential, alternator, A/C compressor attached and swap them to the other engine while it's out. Change all the differential seals too (they're a bitch to pull out). Remove the throttle body to avoid damaging it (good thing I had a spare
). I would even recommend removing the intake manifold to give you even more maneuvering room. Check your exhaust manifold for cracks (both of mine were cracked
). Install a new water pump, thermostat and water temp sensor. Clean the CPAS or replace it if you see oil in the connector plug. Be patient. It's not a '70's car. It has a LOT of wiring, hoses and connections so keep track of things.