18 warlock 1 fvs 1 sorc is the idea (Fiend Pact)

1fvs for scourge and crit, 1sorc fire power and fire crit

the questions about it are a lot since i like the idea but is hard to applicate it good...

1. 1fvs and 1sorc is really better then pure warlock?

2. could be a dwarf con based to let him be tanky, or human int based to raise spellpower.
in both cases not raising cha will lose DC of Eldritch Blasts..
is that really a bad thing? dont wanna spend tp for a +1 lesser heart (pdk will solve this problem about cha)

feat will be the classics:
shield mastery line
empower maximize quicken (extend)
spell focus evo line and wiz past life to support DCs
(((((or mental toughness line for critical raise)))))
insightful reflexes if there is space

epic eldritch blasr
OC
Epic arcane eldritch
Ruin
Hellball


any hints and ideas to get this build better?