I dunno man.. it's a holy city plus protective, that is gonna hurt. I think you prob could take the city but your gonna need a barracks and massive troops, I'm not sure it's worth the casualties but it's up to you.
I'd def go aggressive with your initial settler he's got a holy city right near the yellow city and his culture could block it off or he could settle it himself, with the addition of his imperialistic trait if you want that yellow city your gonna have to do it now, if you don't get it I think it'll limit your city sites.
I think you should go the yellow then red cities aggressively then tech towards priesthood after monotheism via Knightowls paths, build a barracks and start alternating your builds between axeman, infastructure, and one or two spearman to be safe, then hit his capital hard, I'd attack prob around the time you get the oracle done or soon after.
Alternatively I think you could hold it off till cats which may be a good idea considering it's a holy plus protective but then your gonna have several established cities to take in addition, so it's up to you.
Lastly you could forgo everything focus everything on axeman utilizing slavery and everything you have at your disposal and hit his capital hard and fast blitz style before he has a chance to do anything, he'll prob go for some early settlers being imperialistic so it may be an option but it'll set you back on the oracle and infastructure.
I would also add Knightowl has helped me with some beelines for Justinian and I found him to be a fabulous player and I back his thoughts... but, I'd remind you just because it is possible on paper it may not always be the best option, you may or may not be able to pull it off while still going for the oracle, I think it's your call and you should weigh all options.
Keep your composure and think about it analytically, don't let a pretty pixel sway you like most men, it's usually the ch ink in our armor after all