1. That is correct!
2. Not permanently, no. There are some items retiring, but they are 'soft retiring'. This basically means that they won't be as easily obtainable as they are now. They will still be obtainable but more expensive, harder to get and probably luck-based. I don't think plans are definitive yet, but last i heard the devs were planning on a sort of 'event box' that would cost a pretty penny and will randomly award a single soft-retired item from a previous event. As an easy reminder, retiring items have the event and year in their description (2024 Goldsea Seasonal). For this event specifically, the two elandi and two chameleon companions, as well as the radiant apparel set will be soft retiring. The companions under 'Goldsea Companions', the other apparel and the specialty items will return each Goldsea event (once per year). The remaining companions will return with every pack event (every 3 months)
3. I always try to get one of each item, and afterwards I would mostly focus on the items that are soft-retiring. The other items will return each year, so if you want doubles you can always get more of them later. If you do not get enough tickets to buy on of each, I'd focus on the soft-retiring first and the ones specific to Goldsea second.
Side note: Do not buy more than 1 of the specialty items (forum banner and forum decor). They are soul bound* and you can only use one per account, so any doubles will just rot in your inventory forever.
*Soul bound means you cannot sell or trade the items away.