Why does MultiAdd think I am not sending any items?
Ok you're getting there, but your form syntax is a bit off.  MultiAdd needs you to post a form with an array named items.

Here's an example of precisely the sort of thing you need to post:

action    
multiAdd/multiAdd

items[1][purchasableId]    
854
items[1][qty]    
0

items[4][purchasableId]    
857
items[4][qty]    
1

items[5][purchasableId]    
858
items[5][qty]    
0

items[6][purchasableId]    
859
items[6][qty]    
1

redirect    
/cart


So you're posting items, each keyed by an index value to keep the attributes together.  This can be anything really.  You just have to send for each the purchasableId and a qty (if you send 0 the item will just be ignored).

items[whatever][purchasableId]
items[whatever][qty]


Just send as many of those pairs as you need, exactly like that (i.e. it must be called items, and the word whatever you can replace with an arbitrary key).  Each pair must have a value for purchasableId and qty (so for the first example the purchasableId is 854 and the qty is 0, so this one won't be added to the cart).

(You don't need to use the options syntax to add products as such, that's only required if you're using options with those products.  Maybe get your form working without options first, so just adding products) and then we can add them if you need them!)