Although I haven't been to the Fjords, Celebrity was the company that started my cruise addiction. While I do have a cruising YouTube channel that answers some of your questions, I'm not sure if I'm allowed to post a link to it, so I will answer some here:
1.) Drinks package: There's several different levels, depending on your taste and budget. The alcoholic package tends to be the most expensive, and on some cruise lines, if one person buys it, anyone over 21 in the same cabin has to buy it (I'm not sure if this is the case for Celebrity, but I know Carnival does this).
Since I don't drink, I tend to get the soda package, which allows me to have unlimited fountain drinks and in some cases, coffees and teas (neither of which I'm a fan of), For my next cruise, I decided to splurge a little and get the Mocktails package, which allows me to have unlimited soda and virgin versions of alcoholic drinks. You don't have to buy the drink package if you don't want to, as juices and water are usually free. If you reach a certain level in the cruise loyalty programs, you might get free drinks as well. Royal does this for anyone that reaches Diamond level in the Crown And Anchor Society: they preload 4 drink passes daily on your SeaPass/Room Key.
Please note: you do NOT need to use those passes for alcoholic drinks. If the ship has Freestyle machines (which Royal has), when you purchase the drink package, go to any bar and tell them you have the drink package. They'll give you the choice of about 4 cups that have unlimited use for the Freestyle machines. If you choose not to use the Freestyle machines, all you have to do is show your SeaPass at any bar, theater, or restaurant when you order your drinks and your package will be honored. If you have your Freestyle cup with you (Royal Caribbean), unscrew the lid to signify that you want something from the bar. The staff will come over and ask what you want, take your cup and lid, and get you your drink.
2.) Room upgrades: while not necessary, sometimes I do the upgrades just for the experience. One time I won a bid on an upgrade and wound up with a cabin right over the bridge of the ship! Once again, this decision is entirely up to you and your budget. I haven't cruised Celebrity since before the pandemic, but they're owned by the same company as Royal, so the benefits and things are similar. I don't know if they have Freestyle machines now (the last time I cruised Celebrity, several of the ships were going through upgrades).
One final pro-tip: join the Captain's Club. It's the Celebrity loyalty program. You'll earn points towards discounts and perks on future cruises. One of the biggest benefits is they have a status match with Royal's Crown And Anchor Society (up to I think Elite on Celebrity and Diamond on Royal). While the points won't transfer over, the status will. For example, I am due to level up to Elite in the Captain's Club and Diamond on Royal. Once I reach Diamond on Royal, that status will automatically be recognized in the Captain's Club (Celebrity). Conversely, if I reach Elite in Captain's Club first, I'll be recognized as Diamond on Royal.
Another benefit to joining Captain's Club: you can earn points towards your next status before you even set foot on the ship. If you join their email club, they'll send you challenges that you can do at home (this can be anything from watching webinars to doing something on your social networks). If you complete the challenges by the due date, you'll earn a few points towards your next tier.