You are not under any time pressure. Unless you let your totem decay, any bins you drop on your land will stay indefinitely.

Standalone structures (tents and canopies) can store bins, or bins can be placed on the ground or a floor. Some think placing bins in building slots looks neater. Others like me are too lazy to open the building and then the bin.

The only time this makes a difference is in commissaries. Commissaries will reduce the decay of food, but only if it is placed in a bin in a slot. Therefore, your commissary should be a tent or canopy.

As to what you should build first, that depends on what inspirations you get and the blueprints you find. Grind architecture enough and you will learn to make roofs and floors out of sticks and straw. There are rumors of a big bad coyote who can huff and puff and blow Gadu structures down.