1) i like the idea of spearmen > pikemen > musketman. just makes more sense to me. (sidenote, i would make the Tercio a pikeman replacement (so comes with civil service) with the strength of a musketman).
Yeah, I would also greatly prefer it over pikemen -> lancer.
In the vanilla Civ5 pikemen upgraded to musketmen while lancers were standalone unit. But they were useless. So Firaxis decided on a brilliant move to link them with anti - mounted line so we have infantry upgrading into cavalry, field artillery and helicopters

It is awful to upgrade experienced medieval/ancient infantry to such useless cavalry unit, especially for Zulu, Persia and Celts.
On the other hand, it is awful for civs with Lancer units - Poland, Ottoman, Sweden - that they have to wait till atomic era (!!!) to upgrade their unique units.
2)for cavalry, i think horse > knight > cuirasseur > helicopters makes sense. cav can still sorta work as scouts/recon (which makes sense), but they are no longer front line troops. however, MUCH later you can upgrade them to "air cav" if you want... but i would make the upgrade cost even higher. essentially, you keep your cav around for 2 eras, but that doesnt make too much sense to me.
And what between cuirasseur and helicopters?

I would simply upgrade Cavalry to Landships. Armor units are usually considered as 'modern cavalry'.
3) anti tanks should be scrapped. theres no reason to have this unit. it doesnt make sense to have a division of anti tank guns. better left as a promotion.
The only reason to leave them would be IMHO to make them 2/3 range non direct fire ranged unit with high combat strenght (no bonus to cities). So they would be actually dangerous against tanks while remaining useful for other purposes.
5) however, range cav should be its own line. it makes no sense for all civs to have one unit at the beginning of the game and thats it. i think chariot archers should either be removed (for consistency) or be fleshed out to upgrade to the horse archer (no longer a hunnic unique) with construction (same tech as composite bowmen), which in turn should upgrade to a carabinier (current "cavalry" unit). but i think this should be the end of this unit line. similarly, i would make this line have a range of 1, but be able to move after attack. seems more justified to have the 1 range here, as the move after attack makes these units fill an ACTUAL role.
Well, for me it seems to be too complicated, the same as for the current anti cav line

Much better solution - I have even seen a mod like this - is a conversion of 'ranged cavalry' promotions into 'cavalry promotions'.
6) tanks. landship> armor (current tank) > Main Battle Tank
tanks should be new with the landships. they should have a higher strength then they do, have a special "armor plating" promotion that reduces damage taken from all types of infantry (ranged and melee... unless they have the "anti-tank" promotion, which negates "armor plating")
Cool idea.
9) cities: should have range of 3. (and a slightly reduced strength)
think about it. this way, you need to plan your sieges better if you dont want to lose your army. you bring melee units (good bombard defense) up first to absorb incoming fire. you follow up with archers that can still range attack cities from a distance (which makes sense... this is the major argument against archers being range-1 units IMO). you only bring up your vulnerable siege equipment after you have the situation under control. the final stage of the siege is archers AND siege units firing at the city while melee units wait for their chance to storm it.
I think it would be too much - the entire concept of city bombardment is strange and makes wars more static than they were in the history, shouldn't be buffed more.