I am having trouble getting the new engine to start. I may have added too little oil with the low oil sensor keeping the engine from cranking. How much oil does the engine require? how do you know if you have overfilled with oil?

I dont think its to do with the oil, check if you have spark, if not replace the crank sensor

Is there a spark at the plug?
Is there good induction and fuel reaching the combustion chamber?
Is the choke, strangler or cold start working?

An engine needs compression, timing, the right amount of fuel a good spark and a decent cranking speed in order to start.

A side valve easy start engine is likely to have a low compression pressure as would an ohv engine designed to run on poor fuel. Other types of engine with low compression but a good cylinder leakage results probably has a dry or fuel-washed bore and adding a little oil into the cylinder can improve matters.

Depends on why it overheated. If it's dangerously low on coolant, your car may have a sensor that will shut the car off. It's a safety feature to keep you from damaging your engine. l'm sure it also has one for low oil pressure. If it overheated recently, it may not crank. If you have a temperature sensor, it may not be cooled off enough to start it safely. Make absolutely certain you've got enough coolant and the right mixture in your radiator/cooling system, and make sure the oil level is full. Low oil can also cause your engine to run hot.

If your oil is too low or even a little bit low or if your machine is sitting on an incline, it will start and run until the oil is dispersed within the motor. Spreading the little amount of oil that is in there all around the inside of the motor would then reduce the amount of oil that is "sensed" by the "low-oil safety shutoff" switch, which would then shut down the engine. Its possible that your "low-oil sensor switch" is bad. You can test it by unplugging it. Just look for a wire that runs from your ignition switch or ignition coil to a sensor mounted on the engine block somewhere. Usually, it just unplugs right at the sensor. Simply unplug it and crank the engine and if it keeps running, then you know you have a bad switch (if you've topped off the oil, of course!).

Should be on or near the fuel injector supply rail.

02 sensors will not cause your vehicle to stall if they are bad enough to stall vehicle then your check engine light would be on. if the oil level only reads when vehicle running then ADD OIL ASAP. the level is very low. your dipstick checks level in pan once all oil drains back to pan with vehicle off. your oil is constantly flowing when vehicle running. that flow is splashing the oil up high enough that you are seeing it then. once truck is off all the oil drains down to pan and means level is so low not hitting the dipstick. If no reading when truck off you may need atleast 2 quarts of oil. Start by adding one quart to see if you get a reading. keep adding until you do. do not check immediately after shutting vehicle off. you have to give the oil time to drain back down to the pan. DO NOT KEEP DRIVING THE VEHICLE THAT LOW ON OIL YOU WILL BLOW YOUR ENGINE.

Does your unit have a low oil kill sensor if it does the unit won't start if the oil is low also if the sensor is bad that will kill the power. I do know if this may be your problem but check the oil level. good luck.

The trouble you are experiencing could result from several different things. First, check the oil when the engine is cold and completely settled in the sump. You do not want to overfill the engine with oil. If the oil is on the full line (not above it),then the low oil sensor is not shutting off your engine. The oil level should be exactly on the full line-not above or below. Second, remove the spark plug and clean it with a small wire brush or sandpaper. If you are unsure about how to clean the spark plug, replace it with a new one. If both of these procedures have been performed and the mower still doesn't run correctly, the problem is almost certainly with the fuel supply, fuel quality and/or carburetor.

engine could be seized

Was the oil low before you added any? What computer check? You went to a shop to have it scanned? Have the code issues repaired first then move on to the noise issues. Not a very new car I hope your not the original owner because you should not have these problems if you maintained it over the years and don't have 250,000 miles on it. If that's the case get rid of it