I have been an observer of modern for the past several months, and this week I finally made my way into the format, took a deep breath and just jumped right in. The Golgari CoCo Elves deck is my starting point.
While I am running this deck, and after I build my sideboard, I want to starting in the famous...Infamous... shock and fetch lands. The shocks I have so far are (2) overgrown tombs, (1) steam vent and (1) blood crypt. My question is, When building up my land base, is it smarter to start with pairs of each? I don't know enough about the general landbase throughout the decks. At lest for now, the decks I run in EDH are pretty heavy in BRG, mainly Gruul and Golgari, and that is my comfort level at the moment. I have been experimenting a bit more in Orzhov.
As far as building a land base goes, 2 of each shock is a good starting place, as they are not too often played as more than that these days, from what I have seen. With fetches, however, you are looking at a playset of each. Probably stick with the ones you are going to use most often or the soonest and go from there.
I feel like I spun my wheels a bit trying to amass 4 each of all the shocks. Definitely just start with the ones you're currently using and 2 should be fine. The fastlands are relevant in the right archetype.