Rule number 1 is not correct as you stated it. You must occupy a country at the end of a fall turn to capture it; it cannot be captured during a spring turn.
Rule number 2 is also not correct as you stated it. There are some limited situations under which you may exchange an army for a fleet or vice-versa, but those are only when one of your units is displaced from its territory and you choose to disband it. IF AND ONLY IF you control enough supply centers to allow yourself to build a unit following this disband, you may indeed build a unit. It is also imperative that this unit be built at a home supply center, not at some location that your displaced unit might have chosen as a retreat destination. That wording makes me want a vacation. D'oh!
As for your third complaint, you are correct. The two units are stronger than the one unit, regardless of whether the one unit is ordered to attack another unit supporting the move. However, that support can be cut from a fourth unit (as you mentioned) and the holding unit can be permitted to stay in its territory as long as some fourth unit supports its hold. I've played far too many games on this site for the short time I've been a member, and yet the game's code has never shown itself to be inconsistent with that rule.
If you do not like the official rules of Diplomacy, there is nothing anyone on this site can do to save you. However, if your criticism is directed at the site's programming because you think it is inconsistent with the rules of Diplomacy, then you have a bit of a problem on your hands. That said, if you're willing to find people who wish to play Diplomacy under your customized set of rules, then by all means do so.
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