The Tavern

Are there points where increasing skill ups makes no sense? On a weapon for instance, still skill up after minimum delay? Is there a point where more fighting, dodge, armor stop making sense?

Not really. Having more skill generally improves one aspect or another all the way up to level 27. However, there is a point of diminishing returns or more importantly opportunity costs. Because skills cost a lot more to raise at higher levels, there is certainly a point where you would be better off to stop putting experience into a particular skill and instead round out your character more by bringing up some other lower level skills which are cheaper.

For weapon skill specifically, the minimum delay is enough in a 3-rune game. It's probably almost always enough in a 15-rune game as well, because you most likely get more benefit from training something else.

There are clear breakpoints in weapon-skill, as mentioned above. As far as I know there are no relevant breakpoints in fighting, dodge, armor skill. (Technically you can optimise to make the amount of AC, EV & hp round up, but I don't think that's worth the bother)

As mentioned above there are specific weapon levels where a weapon reaches min delay. Fighting, armour and dodging can really be trained all game. As an arcane marksmen you can pick up spells as well, but it may be simpler to win with pure range. If you do go pure range, the only spells I would highly recommend learning are portal projectile, apporation, and blink (others can be used as well, but its highly context dependent). I'd aim to have fighting as the highest stat in general as more hp is generally the best defense when things go wrong.