Oil Pressure Sender Removal ... How Much Oil Will Come Out?

Almost none, unless the engine is running.

 

Sending units are inexpensive, worth changing. You shouldn't have any oil, except what is in the sending unit.
It's not under pressure when the engine is off.
I had one on my Chrysler that seemed to be just weeping. It wasn't. Once you start driving and under load,
more oil will come out, and faster.
Fairly easy to change.

 

No problem. Everyone needs a little "push" now and then.

 

Be aware that you need a specialized "oil pressure sender" wrench socket or you risk the distortion of the crimped area around the insulator, if it is not tightened correctly. That's the same place where the original sender would have developed the leak.

 

Maybe it just needs reseal? Would there be codes if it was problematic? The attachment has test procedure, torque value, and sealant spec.

As a mostly arm-chair mechanic I'm reluctant to argue, but the attachment just says "24 mm deep socket".

 

You could put some teflon tape on the threads, but since it's a tapered fit, you shouldn't need anything.
I also think they put some sealant on the threads.
I don't remember what size mine was...

 

If it ain’t broke don’t try to fix it

 

The leak is not likely from the threads. Universally, almost all oil sender plugs use 1/8 tapered SAE National Pipe threads, even if they might specify a metric standard. OEM sealant with NPT are not likely to leak. The "o" ring or washer between the plastic insulator, phenolic in earlier days, polyamide (Nylon) or polyoxymethylene (Delrin) in current models have much higher coefficients of expansion than the mild steel body. High numbers of heating and cooling and high to low pressure cycles over time degrades the elastomeric seal between the plastic and the metal. Movement and friction between the components will "saw" away the contact surface. Notwithstanding that effect, aging of the elastopolymeric seal will cause it to harden and oxidize. That first results in a weep and eventually a leak.

 

Famous last words that result in catastrophic failure in airplane crashes and loss of life.

 

Or worse if it’s a failed diy

 

Not only with DIY but with many certified professional mechanics. The NTSB record and those records of many other investigations have revealed those facts.

Just look at the current issues with the Boeing 737 max,

 

Here are two famous examples:

First, a 30+ year old "one time use" $2 locknut was reused.

2011 Reno Air Races crash - Wikipedia

One of the longest operating airlines went defunct due to poor and maintenance shortcuts a la "if it ain't broke; don't fix it" mentality.

Chalk's Ocean Airways Flight 101 - Wikipedia

 

As long as you got it changed and didn't strip the threads, you did it right!
It doesn't have to be super tight because it's tapered and will sealed by force.
You can use Gunk to clean the area and rinse it clean. Then drive it and see if your leak is gone.
Which I imagine if it was the sending unit, it will be.