1) is there any way to have the AI play part of my forces?
In the hotkey P Preferences screen, there's a button for 'Automatic Sub Ops', but most players find its performance is sub-par. There's also hotkey H Auto-Convoy system, where bases can be set to use available transports & escorts to move stuff around - although this thing has been improved in the patches, it can be clunky.
2 things are very useful, tho' they're not part of the AI:
a) CS Convoys, you create a TransTF at a base, set it to load consumables, then give it a destination. At this point, you can change it from 'human control' to 'CS convoy', and even set it to load a 'return cargo'. For example, 3 xAKs & an escort load supplies at Perth for Port Headland, unload there, load resources & return to Perth. Then they do it all over again. Very useful for off-map convoys between, say, East Coast USA & Cape Town.
b) Patrol-Zone TF movement, you set a TF such as Subs, ASW or Surface Combat to move between as many as 3 hex-destinations, they'll continue to travel between those points but will return to their home-port when they need to refuel or re-arm.
Both these methods are essentially 'set & forget', but need periodic monitoring as normal travel-damage accumulates over time (except for trips between off-map bases).
2) Is there some trick you guys use to make it all more manageable?
hmm, maybe write down a set of some things you want to do at the beginning of every orders-phase, such as check the hotkey S ships screen for ships w/ high damage, & check the hotkey A & N screens for airgroups w/ high fatigue & low morale, before you get into giving orders to all your stuff.
another technique I use, is to set a monthly rota for visiting your airgroups. Say, the 1st day of each month, you check all USN Fighter groups, the 2nd day might be all Chinese Bomber squadrons, the 3rd day is USArmy transports, etc. Examine all possible factors, do they need training, new pilots, can they upgrade, should they withdraw from combat, can they move up to the front, do they need a better leader, does the base have enough air support, etc. Pilot training is a huge part of the game, often you need to mass-move pilots between multiple sqns, it's a real click-fest that is overwhelming unless you divide it up into manageable segments.
It's worst for the Naval Air, b/c the carriers must be in port to upgrade planes & get/trade pilots. So you might want to plan for an advance date, every 3-4 months, when ~80% of your CVs are in port, & you can work w/ those sqns all at once.