Set looks good, glad the GW is up.
Techwise, Iron working will be very important both to find Iron and chop jungles. However we still need Fishing for Vienna, and Pottery.
We need more scouting so we can make good decisions about city placement, to find metal, and start sizing up our opposition.
As for our next site, here are a few dots:
(I just noticed this screenshot misses a couple BFC resources: Blue's BFC contains Silver to the and Cyan contains Banana - sorry for the poor zoom)
I wouldn't go with Blue next. Silver is nice but Blue doesn't advance our borders in any important direction, we have another option for horses, and overall its a weak site, plus it would need Fishing and a border pop to get any food. I would rather backfill this site later.
Cyan is a very nice site, but it really needs Iron Working so we can get Rice and grow. Nonetheless it would hook up Horses without a pop, and we could chop some infrastructure in the mean time. Also very strong border expansion.
Green is a decent option to claim horses and marble, but its lacking food. However, its got 4 grassland riverside tiles and lots of trees to chop so it could be a good slow growing commerce city. Defensively, its on a hill and firms up our Monty borders.
Of those three options, I would choose Cyan next.
Thinking ahead a bit for city specialization:
Prague: Food/Production? It only has two hills, but it does have cows.
Vienna: Commerce with Cottages
Aachen: Food/GP/Production
future:
Blue: Dunno, weak production?
Green: Commerce
Cyan: Probably production, could go either way. Has two hillplains + horses for decent production. With 9 grasslands, there's a lot of flexibility later.