Those two arguments are very biased. The first one is only a problem in Christianity, and like you said it's a silly argument, God can be malicious and that solves that issue.
The second one is a bit trickier, because you're making the same mistake you accuse others of making. There are two possibilities, either something can come from nothing, or it can't. If stuff can come from nothing God is not needed to create the Universe (and while physics have been able to prove this, let's look at the other possibility just in case). On the other hand if stuff can't come from nothing then stuff must have always existed, otherwise you will get the problem of where the stuff that did that came from, and that applies to God too, so of you can ask "where did the Big Bang came from if there was nothing" you can also ask "where did God came from if there was nothing", so in this scenario you also don't need God, because if it can come from nothing then other stuff can also come from nothing so we're in the other scenario.
Also those are two of the weakest arguments against God, and they specifically go after the Christian God of the gaps. Better arguments against the existence of God are usually about pointing at contradictions in the definition, similarly to how you said nothing can come from nothing but made an exception for God, another example is omniscience vs free will (if someone knows what you will do then you're not free to do different), or omnipotence in itself (can God microwave a burrito so hot that even he can't eat it?), and if we're talking about the specific Christian deity the fact that he needs an innocent blood sacrifice to forgive people should be a clear indicator of the type of being you're dealing with, and it's not an all loving entity.