Line impedance bottlenecks

I’d like to generally know about all the various bottlenecks that a mains feed (and further line) generally has, often by necessity.
I know that a surplus of contact points along the line will raise impedance (mainly contact resistance?), especially if not adequately terminated.
How about the contact compatibility junctions used for terminating an aluminium feed to copper? I’ll have either a 16sqmm copper or 25sqmm aluminium feed installed next spring, wondering if I should just pay the shekels for the copper to avoid potential dissimilarity issues…

Generally when considering a line of given length and gauge, assuming proper installation with the lowest number of surplus junctions, how much approximate loss should be reduced from the resistance formula? Due to contact resistance mainly, I assume.

When considering the formula for wire resistance for a feed, how should I factor in the impedance of the overhead powerline where the AC originates? Negligible? Significant?
Paul estimated that commonly the output impedance of a socket could be as high as 0.5 to 1 ohm… That’s far higher than the simply calculated resistance for my (currently 35 meter 6sqmm) mains feed, considering the first socket from the breaker. It should be about 0.14ohms.
What are all the considerations to note, that could actually raise this impedance significantly?
Does distance from the transformer have a major role, aside voltage sags?

Thank you. Tell me everything!