Technically, you don't sacrifice things to the Legend Rule. They go to the graveyard because of State Based Actions. That being said, the rest of your post seems accurate. You could choose one to go to the graveyard due to the Legend Rule (gaining an extra turn) and then sacrifice the other for another turn so you would end up with two extra turns.
I dont think academy rector is a replacement effect. replacement effects use the word "instead". It has to die in order to exile it, so I think you still draw.
That is absolutely correct. Academy Rector has a triggered ability when it dies, not a replacement effect, so the draw off Skullclamp still happens. However, if a Commander is killed and is put into the Command Zone instead of the graveyard, that is a replacement effect. In that case, you would not draw because the commander didn't "die"
On the other hand, you could cast Cryptic Command in response to the triggered abilities of Hamletback Goliath. This way, the opponent either lets his Brion Stoutarm become tapped, or sacrifices Hamletback Goliath before its triggers have resolved.
I have noticed a recurring confusion over the way Planeswalker abilities work. Most people seem to understand that you cannot respond to the cost of adding or removing a loyalty counter when activating an ability, but they seem to extend that into a belief that the ability itself can't be responded to.
A recent interaction that seems to cause confusion is when Player A activates Sarkhan, the Dragonspeaker's +1 ability, and Player B tries to Hero's Downfall it, Player A thinks the ability happens instantly and that Sarkhan is already indestructible before they can respond.
You are correct in that regenerate creates a shield that is "used up" the next time the creature would be destroyed. When the creature does regenerate, it is removed from combat. However, if you are doing this during combat, and there isn't anything like first strike or double strike on the opponent's creature, both creatures would deal damage at the same time.
So your creature would be dealt damage at the same time your creature would deal damage to your opponent's. Yours would regenerate and be removed from combat at that time, but it has already dealt its damage by that point. Removing it from combat doesn't undo the damage already dealt.
First off, I agree with putting cards into Perfect Fits. I just went through my entire collection (about 20,000 cards) and it was a pain to do it all at once, but it is well worth it when moving cards between decks. I used Ultra-Pro Pro-Fit sleeves and the quality is good, but they were not all cut the same. Usually it wasn't a big deal, but sometimes the sleeves were a little too large to fit into a normal sleeve. Just something to think about.
As for the storage, if you plan on having a small number of cards, you could either go with a 1000 count box or get the 3200 count box as you were thinking. I use 6 for the bulk of my collection and use the 1000 count boxes to store decks in. The other option would be to get a plastic card carrier box. I think KMC makes one. Search for "official cube storage" on the forums and look at page 2 to get a good idea of what others think of this solution. I can't post links to the page.
I like this idea for small collections (even 2 or 3 isn't bad) but it is more expensive than just buying a 4 row 3200 count cardboard box.
That is absolutely correct. Academy Rector has a triggered ability when it dies, not a replacement effect, so the draw off Skullclamp still happens. However, if a Commander is killed and is put into the Command Zone instead of the graveyard, that is a replacement effect. In that case, you would not draw because the commander didn't "die"
A recent interaction that seems to cause confusion is when Player A activates Sarkhan, the Dragonspeaker's +1 ability, and Player B tries to Hero's Downfall it, Player A thinks the ability happens instantly and that Sarkhan is already indestructible before they can respond.
So your creature would be dealt damage at the same time your creature would deal damage to your opponent's. Yours would regenerate and be removed from combat at that time, but it has already dealt its damage by that point. Removing it from combat doesn't undo the damage already dealt.
As for the storage, if you plan on having a small number of cards, you could either go with a 1000 count box or get the 3200 count box as you were thinking. I use 6 for the bulk of my collection and use the 1000 count boxes to store decks in. The other option would be to get a plastic card carrier box. I think KMC makes one. Search for "official cube storage" on the forums and look at page 2 to get a good idea of what others think of this solution. I can't post links to the page.
I like this idea for small collections (even 2 or 3 isn't bad) but it is more expensive than just buying a 4 row 3200 count cardboard box.