Hi New, and welcome to Cruise Chat.
I always suggest that one arrives in the debarkation city the day before the cruise. Particularly when flying to Alaska, this is important because of the looong flight and time difference unless you live on the west coast. Even so, going into Anchorage a day prior gives you some wiggle room in case of airline delays, cancellations, etc.
Anchorage is a nice place to walk around, have salmon for dinner, or visit the museum or the shopping mall the next morning.
The cruise line usually transports you from Anchorage to Seward on cruise day. Even if you make your own air arrangements, you can arrange transport through the cruise line, which often includes a stop at Portage Glacier on your way. The drive from Anchorage to Seward is about 3 hours.
Your travel agent already has the price that Holland America will charge you for their air arrangements and transfers. The agent has probably explained to you that if you fly in on cruise day, Holland America, like all cruise lines, can put you on any flights they want, even a 6am departure or more than one connection. You can request specific airlines and/or flights that suit you time-wise. If HAL can get those flights for you, they will, but they'll charge an "air deviation charge." This will probably be between $50-$75 per person extra, plus any additional airfare those flights may carry. HAL will tell your travel agent which flights they can get you on, and you have time to approve them, or not, before you are charged.
Similarly, if you decide to fly to Anchorage the day before and still get your air through HAL, you can do that, but they'll still charge you the air deviation fee. Be sure to check airfares on your own, or have your agent check for you, to see if you can find flights that suit you that may be less expensive than HAL's air. Don't forget, however, that HAL's air will include the transfer to Seward. If you get the airfare on your own, you can buy the transfer separately.
I hope I didn't just add to your being overwhelmed!
Congrats on being an empty nester!