first of all exodus aren't bad, hey can be dodge it's true, but you can kite, and they have overall the best stat for a destroyer.
then, you need to have a plan playing white fire. You can rush spam T1 (effective as cybran) or go for some fast T2 (effective as sera). You don't want to set up an hover spam, because there is already a big spam of frigate that will hard counter your hover.
What units should I focus on in T1?
frigate. submarine are only usefull on map where there is under water mexx. if your opponent goes for sub, you can set up some torpedo defense in base, and kill all his mexx that are in range of your frigate. (+ you may be able to kill his BP in his navy base with only a few frigate).
When should I go for T2 navy?
it depends of your goal. as i said, you may want fast destro as sera to counter opponent frigate. What i would advise you, is to wait until opponent get to T2 navy. Then you can go for the upgrade. This way, you would have invest more into eco earlier, and you would be able to get the destro in time to counter his destro.
Which units should I focus on in T2?
i advice you to go destro. T2 subs are only viable if you rush the T2 navy, to have T2 unit in the field faster. or you may want to spam T2 subs against uef, if you notice that he has no torpedo boat. (and you hide T2 subs, until you have enough to do a lot of damage).
How many sonars do I build and where?
on white fire ?? only 1. but i feel like it's usefull to have a T3 one only for cybran. you can go for the T2 one for sera, it cover the whole map i guess.
What would be a better question is to know when you should go for sonar. As cybran if you want to go for torpedo upgrade on com, it require lot of e, that you can use afterward for the T3 sonar.
Should I build Torpedo launchers?
you should build T1 one in emergency in your base to defend a frigate rush (you will still lose vulnerable mexxes, but your naval production will be safe).
and you can build T2 one for defending a reclaim spot, after a navy battle. those reclaim spot are the most important thing on white fire. try to have air supremacy if you go for some T2 torpedo defense, so that you can use their personal-stealth. T2 torpedo defense are good against sera destro.
Is T2 PD and Artillery any good against ships?
there is maybe a way of rushing T2 com, and building T2 pd on island to kill opponent naval base. artillery is goodish against destro, but not on a map like white fire (i've never seen one), it's more use for the "rush me more" map.
How important are shields? (Bulwark or Asylum)
asylum is extremely effective, but you will lose the ability of dodging. That make aeon destro super good against sera destro. (you can't dodge them anyway). i still recommend you to go for T2 land and asylum, at some point in the game. (it's better than the costly T3 transition). You may want to get shield disruptor against uef to put their bulwark down. So T3 land is a good way to go. (T1 naval --> T2 naval --> T2 land --> T3 land --> T3 navy; that can be a good gameplan against a uef, be careful of his T3 transition though)
Bulwark is really usefull tool too. Make even harder to snipe cruiser with air. And there is interesting micro to do with bulwark so you can attack and retreat. (there is less fear of attacking, and then you can retreat and get a naval fight on your side of the map, which is one of the most important thing on white fire : having the reclaim close to you)
Should I use Infinity Class Cruisers or Intercepters/Swiftwinds for Air Defense?
if we are still talking about white fire, then you should spam inte. you may want to get some cruiser if you see opponent is T2 air.
I don't recommend you to go swiftwinds, because it's less efficient than inte. Their goal is to defend strat bomber, or you can use their speed to stop some T2 drop on bigger map. They aren't interesting on white fire because of the size of the map.
