There is nothing wrong with spoiling him and don't let anyone tell you that there is. As for the Cry it out method, I don't like that never did, and didn't use it with my son who is 3 and I won't use it with my 8 month old daughter either. I nursed my son (who sleeps in my bed, we're a co-sleeping family) I nursed my son during the night until he was a year and a half, so a bottle every now and then isn't that bad in my eyes, does he need it, no, but he might be wanting itcause of the new baby.
there is a great book, the no cry sleep solution, you should get it.
as for the rest, first congrats on the birth ofyour new son...
I say, give your 20 month old tuns of attention and he will see that you still love him as much as you did before the baby came, and I think that if you just let him cry it out it will make him think that you are ignoring him,
if you used the cry it out method before the baby was born, then fine if that is what you like, but if you haven't, don't use it now, trust me, it will make him think that he is being replaced, and could hurt him in the long run.
I say the best bet is what I said before, give him tuns of extra attention, and encourage him to touch and look at the baby, and hold him, while supervised by you of course, tell him how the baby will get bigger and they will be able to play together, and your son will eventually get used to him.
good luck!
D.