What is the max amount of warframes and weapons can you have, without spending Platinum? I know that EXP is only earned from non-maxed out items, so I am building weapons and Warframes so I can start leveling again. What is the max amount I can have? I am overall rank 3.
I don't recall how many Warframe and weapon slots you start with (I've bought several expansions for each), but here's how you can check how many you have of each:
edited for update 10 UI overhaul
I think you start with 2 Warframe slots and 6(?) weapon slots.
There is no limit on how many frames or weapons you can have, but you will have to spend plat to get more room or sell old frames and weapons.
You can also have multiple of the same, but you only get Mastery Rank xp the first time you level a frame or weapon. Having multiple of the same weapon will not give you more Mastery Rank xp.
Currently there are 16 frames (14 normal and 2 prime) and about 89 weapons in game.
If you level them all you will reach rank 12 and be 6000 points in to the rank.
So in other words to reach rank 12 you either need all weapons and 15 frames or all frames and miss out on 2 weapons.
There are currently 4 weapons that are no longer available in game so you need to own 2 of those weapons to reach rank 12. The weapons you can no longer get are Lato Vandal, Braton Vandal, Snipetron Vandal and Snipetron.
In addition to these answer, there were ways to increase your inventory slots without spending platinum.
When DE grants Event Weapons (anniversary, event, etc.), all weapons supplied will come their own Orokin Catalyst, complete with a Weapon Slot free of charge. This means that even if you sold the event weapons (don't know why you would), you'd have a nice extra slot to store your weapons. This means that these are essentially free slots.
So past events that have granted Weapons w/ weapon slots:
This means that if you were around since Warframe started, and did each event to receive the weapon rewards, you would have:
for a total of: