Two suggestions

An air base can be used to overrun your provinces. A naval base can't.

How can an airbase be used to overrun a province? You mean by having bombers there to support a ground attack?

Regardless of the capabilities, it's wildly unrealistic that an airfield should take 18 hours. It's even more unrealistic that a naval base should take 15 minutes.

a level 1 naval base probably looks about like this:

So I can see that going up in 15 minutes.

Where as if an airbase can be done in 15 minutes I can scour the earth with my planes just as fast as an armored car on forced march will go. In a tactical retreat situation I can try and hold an airbase position while some forces are embarking or disembarking or otherwise getting out of the range of a plane. If the planes can reach me within 30 minutes of a province being captured 400 km away you lose that defensive depth.

i think it still could take a little less time for an airbase to build, around 14 hours not 18. And a naval base should still take maybe 2 to 4 hours, I mean the image u showed, could u build/launch a submarine from such a "naval base"? I think the point is reasonable, but not as bad as some make it look.

Well and the first point, the resource research? I mean it could be a thing, but don't see a reason for that.

Max it should do is let first of all (in my opinion) research each building.

So researching infrastructure or an industry complex, it will boost their abilities, which will then boost the production of researches and other things...

A level 1 air base becomes operational in 9 hours.

Another thing to consider is that often your air bases can be captured without being completely destroyed. So, depending on the percentage of damage, the enemy can repair the air base and can often use it against you a lot sooner than 9 hours.

At 50% damage, a level 1 air base would still be usable (though vulnerable to damage).

if you have been on the receiving end of such an attack, you would see that building up airbases faster is a double-edged sword. Nice if you have local air superiority. And horrible if your enemy has local air superiority.

I like that too. Often times I had to very slowly build up an airforce suitable for attack simply because my airbases are still building. I would suggest 10-12 hours building time. As Lawrence Czl said, this may be exploited by your enemy, so I'm more like so-so agree on this.

Yes having a research tree for resources would greatly help the game.

Some examples include maybe improved extraction or improved drilling etc.

This would make the game better in numerous ways.

resources tree will help advanced countries to be the strongest economy as in reaal life

cough propeller planes don't even need steel mesh, they just need a flat surface cough also, just reducing the time to produce the air field by four hours doesn't do much, it would be nice to see 15 minutes to make both though.

I like the idea of creating a research tree for resource production. For example, you can research level 1 oil production and that would increase oil production by 10%. Level 2 oil production can be +30% and so on. This is significantly improve the game experience for me.