I figured there might be quite a few other people new to Commander who might not have dabbled with Slivers who might also be interested in building a Sliver Commander deck, so lets all take a look at what could make a sweet Sliver deck
However, if you don't want to immediately lose those copies to the legend rule, you either have to make copies that aren't legendary or shut off the rule altogether
MTG Vigilance Rules What do the Magic rules say about vigilance
Even then, the payoff isnt all that great
Counterspells like Mana Drain, card draw effects like Brainstorm, removal like Reality Shift and powerhouses with alternate casting costs like Cyclonic Rift are at your fingertips for a mere 3 mana
If all the other decks are making 1/1 mana elves or 2/1 beaters then doing either of those things is tempo neutral, making a 2/3 is tempo positive, while doing nothing is very tempo negative