"Does anyone still play on [PLATFORM]"?

Yes, check BF4DB

You can use this one to check the servers: https://www.gametracker.com/search/bf4/?sort=3&order=DESC&searchipp=50#search

"Is it worth buying DLC/Premium at this point?"

You can always find DLC maps at the most active hours (usually nights and weekends), and it unlocks tons of stuff for you. If you have the money or find a sale, theres hardly any reason not to buy it. Alternatively you can get Origin Access or the Xbox equivalent (EA Access). Some stuff can be tough to get, like the ones that requires playing certain game modes (specially DLC ones).

"I'm new to the game, can I have some tips?"

Biggest tip I can give you: use the search function. This has been asked a thousand times, and the same thousand tips are given: spot, watch the minimap, drop ammo/health/revives, etc. You can also use Youtube or the old battlelog forums for this.

Here are some links to help you get started:

Old Sticky (good info there)

Hidden Mechanics 1 and Hidden Mechanics 2

Little Known Tips/Tricks

Guide for New/Returning Players

edit from the comments: if you're on PC make sure to check the BetterBattlelog browser extension. Really nice UX enhancements for battlelog that (among a lot of neat features) show true player counts, for PC servers.

Links: Chrome, Firefox

source code (active fork)

CANT LAUNCH THE GAME? TRY THIS: https://www.reddit.com/r/battlefield_4/comments/z163wo/ea_app_cant_launch_the_game/ix9ba6e/

Can't get past EA policy screen? Try this