You mean there's more to space marines than just infantry? so I have an all infantry armour of around 100 marines when I could have freaking tanks? ZOMG! yes, you can have around 100 marines for about 1500 points, then upgrades, terminators and what not later. if you don't know, there is no way in hell I could collect 100 marines, I just said that for my Warhammer crazed friend.
Also, Lego Grey knights are easy, just try making a halo spartan in grey armour (duh) give it a knights helmet and oversized melee weapon and presto! one grey knight! no ranged weapons because ranged is fo' sissies and stormtroopers!