I’d say keep it for when you really need it, and you will need some at some point. As others pointed out, inventory slots are the biggest plat consumer, and as you expand your arsenal, you will feel it. Then is catalysts and reactors, which normally aren’t available in large quantities - i’d say buy catalysts but wait and be patient with reactors, as they have a much lower consumption rate and you’ll eventually get all that you need for free.

Honestly I’d hold on to most of it until you get a feel for the game. Spend a bit of it on slots (though you can sell most of the early weapons once you master them, they aren’t that good), and once you start getting weapons and frames you like orokin catalysts / orokin reactors. Then, once you know what you hate doing, spend it to avoid doing that thing to farm something.

If you want to splurge on something early, buy the prime version of a frame you like (or like the look of) off of http://warframe.market. Prime frames honestly aren’t that much better than the regular versions, but they’re tradeable, and being the best version of what they are it’s easy to justify investing forma and orokin reactors in them. Note that you’ll still have to build the frame, so make sure you have or can get the materials required for the blueprint.

My first riven roll i got early was like 800p (im f2p). So what i purchased was slots for weapons, frames. I finished few sets, exchanged my parts for the ones that i didn’t have. I bought Arcane Energize rank 2 (still have it, its not maxed cause im poor) that was truly a game changer that i definitely recommend.

Dont spend it without actual need. Use it gradually for stuff you need like slots.

The necramech grind is kinda a pain in the ass. Don’t buy it from in-game market, but at some point buy the parts from warframe.market. other than that slots until you have good enough weapons to consider upgrading with plat.

buy glaive prime and mostly keep it for the ongoing maintenance - orokin reactors/catalysts, slots, maybe some annoying mods that are nice that’d be my advice

Double it and give it to the next Arcane Energize Seller.

That was a half-joke; you could opt to save it and wait until you get around 2,500 plat and get a maxed Arcane Energize. Otherwise, I recommend buying some meta prime weapons and/or frames if you want to spend it immediately.

As another comment said, use it gradually on what you want.

One of the most useful things are slots, warframe slots and weapon slots.

However don’t spend everything right away. You will keep the 1k plat, and you can also trade with other people if they have parts/mods you need (warframe.market) (don’t get scammed tho).

A bunch of weapon and warframe slots would probably be most useful. Save the platinum and buy them as you run out of slots. Maybe a nice colour palette for better fashion or deluxe skin if you have already found a frame you really enjoy.

Weapons you get in the early game are often not worth keeping and that means they are not worth putting a catalyst in.

Save your plat for slots and for investing in gear you enjoy.

The first weapon you can get that’s worth keeping is probably Dread. Atomos, Cerata, fang prime, also stay strong as you rank up, as do the rest of Stalker’s weapons.

Slots mostly. Maybe there is a certain mod/arcane/warframe that would really ease up your grind and add QoL to your life; and is also a pain to farm (or only available too deep into the game) then you can buy it too.

(I remember back when I started Arcane Energize was an extremely rare and difficult to earn drop; whuch also added a lot of QoL; so I bought a bunch using a little plat.)

As for cosmetics. Maybe a colour pack (most amount of customization per plat spent imo). Maybe a skin for the Warframe you use the most.