My mechanic said he replace 3 oxygen sensors.

What were the trouble codes you are getting?

If it is a minor problem that is causing all these, trading it for $1 k is not really a good move.

Yes, the filter being a non maintenance component means it is not necessary to replace it andbeing a trainer type, if it is clogged, it would mean the transmission is going to fail soon.
If there are a lot of gunk in transmission oil pan, you should consider trading in the vehicle as the transmission is not going to last long even if the fluids are replaced.

This is the recommended replacement procedure.

AUTOMATIC TRANSMISSION FLUID REPLACEMENT

Drain the fluid and check if there is any evidence of contamination. Replenish with new fluid after the cause of any contamination has been corrected.

1. Remove the right hand hose connecting the transmission oil cooler pipe to the oil cooler (built into the bottom of the radiator).
2. Connect a suitable length of hose from the radiator pipe to an oil drain receptacle, large enough to hold the quantity of discharged fluid.
3. Start the engine and discharge the ATF.
Operating conditions: "N" Neutral and idling.
CAUTION:
Start the engine and then stop it within one minute. If the ATF is discharged before the one minute elapses, stop the engine at that time.
Amount of oil discharged: Approximately 6.5 dm3 (6.8 qts.)
4. Remove the drain plug at the bottom of the transmission case and discharge the ATF.
Amount of ATF discharged: approximately 2.0 dm3 (2.1 qts.)
5. Install the drain plug and gasket, applying the specified amount of torque.
Tightening torque: 32 N.M (24 ft. Lbs.)
6. Fill with new ATF through the oil filler tube.
Amount of ATF added: Approximately 8.5 dm3 (9.0 qts.)
NOTE:
If the entire amount of new ATF cannot be added, follow step 8 to add fluid.
7. Repeat step 3 to discharge ATF from the hose.
8. Add the new ATF through the oil filler tube.
9. Attach and secure the hose that was disconnected in step 1 and securely insert the oil level gauge.
10. Start the engine and let it idle for one or two minutes.
11. Move the selector lever through all gear positions, ending in Neutral position.
12. Make sure the ATF reaches the "COLD" mark on the oil level gauge. If there is not enough ATF, add more.
13. Drive the car until the ATF temperature reaches 70-80°C (158-176°F) and recheck the ATF level. The ATF must be within the "HOT" range.
NOTE:
The "COLD" level is for reference and the "HOT" level serves as the standard.
14. Securely insert the oil level gauge into the filler tube.

Thank you.

Happy CNY to you too.

It depends on what filter is used. For those with element type filter, yes, it has to be replaced if the fluids are not in good condition. For strainer type, what is the use of replacing a filter that is only mesh wires that do not really provide filtration. Its main purpose is for preventing debris from getting to the system, not filtration and would not get clogged, unless you have plenty of clutch chunks in the oil pan.

Removing the oil pan would allow you to drip dry the interior and allow more fluids to be replaced but sufficient time must be given for the fluids to drip unless you are going to loosen the valve body bolts, which would allow the fluids to drip dry faster.

Otherwise the method in my previous post would be recommended