1) Don't understand what you mean by this point. If you mean what I think you mean ("Tech tanks are too expensive because I'm too busy spending all my fuel on doctrinals") then it's a weird point to make. Whereas you're not going to be fuel starved, you're not going to have any manpower either because you're going to be saving it for the ridiculously priced heavy tanks.
Basically, different resource distribution, relaying on heavy call-ins will leave you floating fuel and menpower starved(or at least strained). Relaying on tier armor would allow you more efficient resource distribution if you wanted to go for multiple tier units and you still could afford fuel-wise heavy tank later on.
There's also a very good reason heavy tanks don't cost as much manpower as that and that's because Relic actually wants players to be able to use heavy tanks without completely fucking over their ability to maintain their infantry core.
Again, look at SI KV-2 for the refference point. Getting it is a huge mp strain, so you can't really spam it as you can currently with "more balanced" Tiger and IS costs. In KV-2 case you can get one and then you need to go back on relying on your tier units. Basically, you can still go for heavy tank, but you can't ignore tier armor if you want to stay in game. That is the point of my suggestion.
2) Well sure. Making them extremely in-affordable would indeed force you to think twice to get them; I don't think the intention of the balance team is to make heavy tanks completely unattainable without flat out sacrificing your infantry. If that was the route Relic would use to make non-doctrinals more attractive than doctrinals then they may aswell take out doctrinals all together because there would be absolutely no point in getting them.
Again, its not about making them extremely in-affordable, but about cost redistribution to force player into different economy, the one that actually have a drawback for skipping tiers instead of raining you with rewards for doing so. Cost values can obviously be balanced accordingly, but as I've said, delaying heavy armor or tying it to tiers will change absolutely nothing.
Like Wooof said, it would actually be far more rewarding to wait for heavies if you were losing as opposed to winning: The losing player could just sit in his base for a few minutes (defending maybe the closest points to himself at minimal infantry MP drain) before popping one out. Currently, this is what you're faced with when you're confronted with the Tiger Ace.
Tiger ace is not strong because it costs no fuel, sure that is a factor, but the real deal is it got vet3, greatly increasing its performance over normal one, not to count ability. I thought that was quite obvious, but apparently it wasn't. If you are being pushed back to base normal Tiger or IS-2 won't save you unless opponent is completely unprepared in terms of AT.
3)Eh. No. I've played enough Tiger Ace games to know that you need very minimal manpower when you've got an all-in-one-tank clearing the field for you.
You know, they don't need to come at vet3 with IWIN button ability against tanks. Tiger Ace is bullshit unit, normal Tiger not so much. They would still be as strong as they are now, you'd just have to give up some infantry presence instead of sacrificing absolutely nothing.
That pretty much covers your doubts as well wooof.
Values I gave can be balanced, I only gave a raw example of resource shift and its implications.