I don't think vacuuming is necessary. You can purge the air out of the pipe, this is more effective and practical than vacuum.

Both will give d same effect bro. One you use vacuum to suck the air out, but this method you need extra tools, which is d vacuum pump itself and its time consuming. Another method is using the gas itself to push the air out of the pipe. The second method is d easiest but its not environmental friendly since you release d gas to d atmosphere.
Bro be careful on your words, not all engineers are smart and not all installer are stupid. In some cases engineer do refer to installer to get a better and practical solution.
Im engineer myself, i respected my technician bcoz they have experience and hands on skills. Which engineer cannot learn from d books.

D most common mistake in aircond installation is d piping insulation. Gas and liquid pipe should be insulated seperately. But most of installer they insulate both pipe using d same insulation.

Its not practical and financially viable to buy all those tools just to install an aircond. All you need to do is observe d work and tell them the right things to do if you have d knowledge. However, If you dont know, just keep silence and let the installer do d job and just accept what ever the result will be.

Ive an uncle, he is an ex army. He built his own home in less then 1 year, in malaysia. Seems like malaysian know how to built house better.

So, what the diff between R410a and R22 that make one need to be vacuum and the other don't?