The Ascension
"Christ ascended into Heaven from whence he will return to Earth."
Where is Christ? He has flesh and bones so he must be somewhere. "At God's right hand" is not a location, it is a status, the "position of authority". He took that place at his resurrection. Heaven is not a place so nobody with flesh and bones can go there.
My short answer is: don't know and don't care! Maybe he is literally somewhere on planet Earth or maybe elsewhere in space. It makes no practical difference. As we say in the Internet Age, he is with us virtually. When the new humanity is ripe he will show up for the fulfillment.
What did he mean by "I have not yet ascended"? Don't know and don't (much) care exactly what he said and what he meant. It's just one enigmatic comment. Maybe at the time it was clearer what he meant. Let's not build too many castles on it! I could invent all manner of interpretations, but I'll leave such ducking and weaving to the Biblicists!
What happened when he "parted from them and was carried up into Heaven"? Again, one verse with no accompanying explanation. Note the "and". Contra traditional interpretation, the ascension was not the parting. It implies that he ascended after parting from them, so they did not see the ascension, they only surmised it.