The number of units per tile is irrelevant as is the number of tiles around a city or any of the other things people are making a stink over. They are nothing more than small pieces of the bigger picture. Without knowing how the combat mechanics work, what promotions (if any) will be available, the strengths and weaknesses of the units themselves all you can do is speculate based on your experience with Civ4. Personally, I'm looking forward to not spending an hour waiting for the AI to move hundreds of units.
As for making a PG mod for Civ5 there will be a lot more to consider than just the shape of the tiles. Granted the square tiles of Civ4 played havoc on ranges that alone won't make you game more like Panzer General, it'll look more like it though
You'll need to mod the AI both to encourage more historical behavior and to adjust for a world war scenario. You obviously don't want Russia building the Eifel Tower when they should be trying to fend off the impending invasion from the Germans in the west. Maybe this will be easier in Civ5, maybe it will be impossible at first, who knows.
You'll need a LOT of custom art assets. If you're lucky and can port over Civ4 models you'll be in good shape, if not... your kinda screwed.
You'll need custom leaders and civilizations. If you're lucky you can cheat and use 2d images like we can in Civ4. If you're really lucky, it will be easy to modify the leaders provided with Civ4 or they'll have multiple era versions so you won't have to try to make Caesar's robe look like an outfit from the 40's or make all of your leaders using Roosevelt's suit
You'll likely need a lot of custom coding to shift the game from empire building over centuries to war over a few years.
Remember the scale too, in Panzer General you weren't moving your units around a hex based map representing all of Europe of the entire world. So you either need significantly smaller scale maps representing a single, small area or you need 'units' to represent larger collections of units instead.
It's certainly not impossible, but it involves a lot more than hex based maps