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.
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.