The base is the plot your Animals stand on, and the label over it is the whole income
There is no separate base screen to open: the base is your own ground, and the per-second label floating over it is the total. In the recorded session that label read $0/s before anything was placed, $95/s once an Animal stood there, $620.94B/s later in the same run and 30.15B/s at another point, which is what makes it the one number to read before and after any purchase. The same session printed placement receipts as Animals went down - Placed Cursed TRex!, Placed Dark King Dragon!, Placed Night Spider! - so an Animal in your inventory contributes nothing until it is placed. Whatever a card says about an Animal's value, the plot label is where the result arrives.
While you carry a stolen egg, the base is the safe zone you return to
The base does a second job during a theft. As soon as the egg is in your hands the game offers two carry buttons, Soltar and Teletransportarse a la base, and the banner tells you what they are for: Trae tu huevo a la zona segura, bring your egg to the safe zone. The spawn and base area carries a white ZONA SEGURA floor decal, so the boundary is painted rather than hidden in a menu. The practical order is therefore: take the egg, cross back, and use the base as the end of the run rather than flying on with it. The recorded session did both - it dropped eggs with Soltar and used the base teleport to bail out of a chase.
Expansion is stated by the developer, and its capacity and price are not published
The only expansion statement found anywhere is the developer's own listing line: Expand your base to hold even more Animals. It confirms the mechanic and nothing else. No surface read for this site - the listing, the recorded sessions, the index or the shop - printed a capacity number, a base level, an expansion price or an upgrade button for it, and none of them showed what the game does when the ground is full. Those are recorded here as unknown rather than estimated. In your own session the place to look is the moment you try to place an Animal: whatever prompt, padlock or price appears there is the only capacity information the game currently gives you.
What the base is not
Three things are easy to confuse with base progress. Capacity is not income: more room lets you place more Animals, but the label only moves when an Animal is actually standing there, so an expansion bought before you own the Animal changes nothing. The base is not where offline earning is decided either - the developer states that Animals generate Cash while you are offline, and that line belongs to the income page, with no rate published for it there. And wings do not belong here at all: every wing card read in the recorded sessions printed a stamina multiplier and a price, never money, so a wing purchase does not change what the ground pays.