What I mean is if something exists…such a love or joy…does that mean God is the perfection of those things?
And if so, does the same apply to things like hate and selfishness?..For example, hate and selfishness exist…would God be the perfection of those things as well?
Yes you are quite correct.
This theme has historically had a lot of attention esp in the Middle Ages by Aquinas (Summa Contra Gentiles) and others.
Look up things like “the Divine Names, Perfections or Attributes”.
Its interesting that the conclusion is that we actually only know (philosophically) very little about God. This is because love mercy truth etc we only know in an imperfect way. And it is impossible for us to understand (a) how each of these are perfectly active in God and (b) how they all become one in God.
Therefore our understanding of those concepts is weak and only “analogical” (partly right, partly wrong) when referring to God.
The Mystics, when it came to this sport of thing, said we are more certain about what God is not than What He Is. You might like to look up “via negativa” versus “via positiva” in this connection.
Finally you mention hate and selfishness, in short evil qualities.
Aquinas had the same problem as you.
With great insight he realised evil does not actually exist in itself. Evil is but an absence of something that should be in something else.
Therefore evil is not a perfection of anything but rather the very opposite.
In fact perfect evil, if it could be perfect, would be “nothingness”.
I still remember my Phil 101 paper in 1980.
The priest professor began by giving us a riddle.
If there is nothing more perfect than God, and the strongest man in the world has a huge hairy chest, … does that mean God’s is bigger and hairier than that of this strongest man?