I'll try to help, but I'll be a bit in the weeds for part of the answer.
I say book as soon as you know your dates. You'll pay a one-night deposit, but the deposit is refundable, I think, up to one week prior to the first day of the reservation. So, it would just cost you a refundable pre-payment of one night to book in advance. Then I check the reservation page of the resort periodically to see if the rate lowers for the exact room on the exact dates (usually when Annual Pass rates come out). Sometime it does, sometimes it doesn't. During HHN, the resorts get booked up and rates tend to climb as they do.
Unless things have changed, and I have not gone this route, so hopefully someone will correct me if I'm wrong, if you book a package all at once, there would be a cancellation or change fee involved if you had to make a change.
Daytime tickets: If you're going four days or more, then compare the price of an Annual Pass. There are four tiers of APs with more discounts and benefits, and fewer or no blackout dates, as you move up in tiers. Otherwise, I'd try to get tickets as soon as possible, since they do not expire. NOTE: unless it has changed, some promotional deals (four days for the price of two) might have an expiration date. Just check the fine print.
You can then add the HHN tickets later when they go on sale. They only go up in price as the season continues, so go ahead and bite the bullet when your choice of ticket is available.
Since you say your trip is in a few years, it's great you are learning it all now. I'd say just do a fake, trial run of checking resort rooms and prices, make notes of daytime ticket prices, and then when HHN tickets go on sale and for how much. I know it can be a little daunting at first, but it's really not that bad with Universal. Just a matter of becoming familiar with they way they do things.
Just to give you an example for our HHN trip this year... I booked our Portofino room in February. Glad I did, because the price has gone up quite a bit since then (and surprisingly the deluxe rooms at Portofino were cheaper than standard rooms at Royal Pacific and Hard Rock at that time). We have APs, so I'll just need to renew them when able to do so, which will be this summer. I bought our Unmasking the Horror tickets when they went on sale recently so we could get the date and time we wanted. Price will not decrease, so get it while you can. We opt for the Frequent Fear with Express, so as soon as those are available, I'll get those too. Then it's just a matter of waiting for the HHN fog to roll in.