2. As SCC said, and yes it as a non-ignorable additional cost. Part of what makes that d-mod so painful, and basically makes Efficiency Overhaul a must (rather than just really good) on ships that have it (especially Cruisers and Capitals).
Just want to point out that while Increased Maintenance is
always an additional cost of running that ship, there are 2 skills available, which if both are taken will reduce the supply cost of a ship with IM to below that of a pristine version. And further decrease that cost for every additional d-mod.
The main part of the mod that everyone always ignores is that it gives you a ship with no additional loss of combat ability, with the only cost being extra maintenance. Which can be mitigated with skills. And since many people will avoid taking these skills due to not being 'optimal', they suffer the full effects of the mod, which tbf are p. bad.
tl;dr
IM is bad if you don't take certain skills.
IM is entirely ignorable if you do take those skills.
Which skills in particular, and whether they are 'worth' being taken will be left as an exercise for the OP.