Usefullness moving forward and TMs

1 FTM and 1 CTM and that Nite is guaranteed to be significantly better.
It may end up with Hurricane, as a worse case scenario but even that is a massive improvement on what you have.

Usually CTMs can be a gamble, and can take many of them to get a preferred moveset, but in the case of that Nite, it is a no brainer.

All that said, it will still only be a very good generalist, but can fit into most teams where you are short of a full squad of optimal counters, and will make a decent gym sweeper.

Well if you already have 3 dragonites with O, DM and H, you don't need another one absolutely. If all 3 of them don't have dragon tail already, time tu use those FTMs. In fact, with your SW/HB Dragonite and you're exactly in the same situation as me (add another SW/DM dragonite). I should TM HB, but since I have more important targets and already have better dragonites with the right movesets, I consider it's not a priority. Actually, SW/HB is the best moveset against grandbull, should it return as a raid boss :D

But since you specifically asked "moving forward for the meta":
- Keep Salamence as is for now ; might be very good against Registeel and Regice (when no ice move).
- TMing Dragonite is indeed a guaranteed improvement, but since you have others, it's not like you're in absolute need of another one right now... except if rayquaza returns this summer, then do it absolutely!
- If you planned on evolving that beldum anyway, do it, see what is its moveset and then decide if it's worth a TM. A steel moveset can be nice against Regirock and Regice.

In any case, I don't think using a TM right now would be very useful. I would say wait a bit and see who is the next T5 raid boss. If Groudon comes back, that means we are in a weather trio rotation and Rayquaza will probably be next, so as soon as Rayquaza is here TM this Dragonite and give it a double dragon moveset. If the regi trio starts, SW Dragonites are actually interesting mons and you'll take more advantage of a double steel Metagross. That said, you don't want HB either against the regis...

I started hording Rare Candy and now it seems like I get 2-4 Rare Candy for every T3 I do. I'm out of Charge TM's and havent seen any drop in weeks. I swear to god , this game nerfs the drop rate on certain items when you need them the most (Ok, I don't really know that but it feels like it)

So my advice is wait until you're in the double-digits on CTM's before using them......unless you have a specific need right now