I was playing around with this idea and you may be right about the land count. 20 is sometimes too little, sometimes just right. Maybe 21 would be good... Especially now with the lowered curve I think 22 is a bit high. May I ask why you are main boarding Rest in Peace?
EDIT: I would drop the Mana Tithe and maybe a few lands (weenie usually doesn't need more than 20), then add 4 Champion of the Parishs, and whatever else you prefer. Go for at least 8 turn 1 creatures I would think.
Modern
URGTemur ScapeshiftGRU
EDH
WGKarametra EnchantressGW
UBGSidisi, Brood Tyrant ReanimatorGBU
UBRKess DoomsdayRBU
WBGGhave TokensGBW
WUBZur RebelsBUW
WUBErtai CursesBUW
WRFiresong and Sunspeaker Spell SlingerRW
EDIT: I would drop the Mana Tithe and maybe a few lands (weenie usually doesn't need more than 20), then add 4 Champion of the Parishs, and whatever else you prefer. Go for at least 8 turn 1 creatures I would think.
EDIT 2: Don't forget Elite Vanguard. And Elspeth Tirel may be better for the 3 1/1s as opposed to 1 1/1.
Modern
URGTemur ScapeshiftGRU
EDH
WGKarametra EnchantressGW
UBGSidisi, Brood Tyrant ReanimatorGBU
UBRKess DoomsdayRBU
WBGGhave TokensGBW
WUBZur RebelsBUW
WUBErtai CursesBUW
WRFiresong and Sunspeaker Spell SlingerRW