The Whole Story on the 2002 Mazda' s no start condition

I bought the vehicle in May 2010 and it quit running on July 29th 2019. After having it towed off the highway, it was inspected and diagnosed by a Napa Auto Care Center technician.
The technician said that some of the cylinders had low compression readings and that there was a timing related issue with the engine. L though that to be a little vague; a timing related issue.

I however asked him to give me an estimate on what it would cost to repair my vehicle. He did but it made mention that the timing components should be replaced, @ a cost of $1,005.

I thought that amount to be more than I could afford, plus in the 60's I had did a timing chain job on a car, so I thought; How hard could it be to do one on this Mazda? Well even though I did do the timing chain and components replacement, it was quit a task without a lift and I also replaced the oil pump.

When I removed the valve covers, the timing case cover and the oil pan, I observed oil varnish in all three places that told me the oil pump might have caused the vehicle to overheat and stop running.

Instead of following my instructors directions that I had received in class, I followed the Napa technician's diagnosis and did the timing chain job, only to find the engine was not out of time, the timing chains were not stretched enough to affect the timing and none of the timing components were in need of replacing.

But I replaced them all because I had removed the timing case cover. Once all the new parts and all the gaskets were installed with the engine in time, the engine would not start.

This is when I did a compression test on it and got the readings I previously stated. I believe that the engine has internal damage to the valves. To me this is indicative of the very low compression readings on five of the six cylinders.

I also believe that if I do a cylinder leak down test on each cylinder, one at a time with the cylinder @ TDC.
The readings will most likely be in the same range as those on the compression test. This would tell me proof positive that there is valve damage and the head gasket on the driver's side is blown between cylinders 4 and 5.

To me if would be more practicle to do this because if I take the heads off that means the heads should be serviced. If I am going to service the top half of my engine I may as well service the bottom half, because it has the same stress, wear and mileage on it as the top half does.

Someone give me some feedback on this. Tell me what you think according to what you know to be factual.