| No. Not true.
You can't believe any more than about .0000001% of whatever you've "heard" about lubricants. It's just amazing beyond almost any other subject, how much witchcraft and vodoo and black magic gets invoked when people start giving their opinions (never backed up by any facts) about oil. About the only other thing that even comes close is electricity. In the case of a manual transmission, you've got some steel parts spinning around, on some roller bearings. This is not something supernatural that requires wizards and sages to decipher.
Use it, it will be perfectly fine.
No you do not need to overfill anything. Take the drain plug out, let it empty, put the drain plug back in, take out the fill plug, fill to that level. Don't worry about "tilted", just fill it until it reaches the plug, and put the plug back in.
Both plugs are on the pass side of the trans. DO NOT remove the thing that looks somewhat like a plug on the driver's side!!! Disaster will result.
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Numquam ponenda est pluralitas sine necessitate.
— William of Ockham, from Quaestiones et decisiones in quattuor libros Sententiarum Petri Lombardi
Roughly paraphrased into modern English, and applied to figuring out what's wrong with your car:
The simplest explanation that fits all the facts is probably the right one. | 
