Kundli matching, with the kootas explained

Conventionally 18 and above is acceptable, 24 and above good, 28 and above excellent. But the composition matters more than the number: 18 points with Nadi and Bhakoot both passing is a better position than 24 points where both have failed, because those two kootas are worth 15 of the 36 and are scored all-or-nothing.

Yes, and the classical exceptions are well documented — the same nakshatra with different padas, the same Moon sign with different nakshatras, or a strong Graha Maitri between the Moon-sign lords. Treating Nadi dosha as an absolute bar is a modern hardening, not a classical rule.

No. Guna Milan compares two Moon positions and nothing else. It never looks at the seventh house of either chart, at Venus, Mars or Jupiter, at the D9, or at whether the two dasha sequences will be in step. Use the score as a screen, then do the actual comparison.

That is the case where a manual reading matters most. When both charts carry Kuja dosha it classically cancels; when only one does, the severity depends on which house Mars occupies, its strength, and whether it is aspected by a benefic. A blanket refusal on this basis alone is not supported by the texts.