1) I don't feel like Combat Readiness 3 is a must. 5% overall better performance is nice, but you can get another 5% for everyone with Fleet Logistics 3. 25% more peak performance time is good for equalising PPT of your combat ships, but isn't necessary, when that particular officer flies the biggest ship around.
2) Carrier skills are all around useful for fighters, so if a captain is in charge of a carrier, he has to have those skills. Incomplete carrier set officers I dismiss, those without I assign to warships.
3) How many carriers do you want? If it works, it works. Carrier spam is perfectly doable.
4) Timid officers are a waste. Cautious ones... I guess they are alright on fragile carriers? I use steady officers for most carriers and fragile ships. Otherwise, warship officers are all aggressive or reckless. They genuinely have the advantage with all their skills, so they should indeed press it.
5) I can't say about others, but in my case, it depends on skills. General preference is to go for levels 3. Combat exceptions areDefensive Systems and Helmsmanship, where I stop at level 2. For leadership, I go full out if I take a skill there, except for a token point spent on Coordinated Manoeuvres. Same with technology and Electronic Warfare, though I sometimes use Navigation as "leftovers go here" dump. Industry tree is where it varies a lot, with Safety Procedures, Recovery Operations and Field Repairs being skills where level 2s are pretty good, but level 3s are good as well. It depends on how much do I want to spend on industry.