First of all I don't believe it's only going to be JWs in paradise. There were Egyptians who left Egypt with the Israelites. Also Rahab and her family were saved.
Why wouldn't people be able to get to the level of technology that we have now, probably an efficient and cleaner version of it in paradise? If we were made in God's image and he's a creator, why wouldn't we be? I've never believed that the paradise would be like that. Obviously in the beginning it would be disrupted but we'll have solar and wind power and all the rest eventually. If it was done before, it can be done again.
And Jehovah didn't exactly leave Adam and Eve to their own devices. If he had no contact with them, why would the Bible mention that after they ate from the forbidden tree, they hid from Jehovah?
As for Jehovah been a magician, he provided mana and water from a stone while the Israelites were in the desert. How about the oil that never ran out for one of the prophets?