Hey !
Even though I am a C++ developer and would care writing custom nodes, in my knowledge you can’t add C++ code in the marketplace yet! For this reason i refrained from using custom nodes and instead used the programmer’s workflow logic (but in BP) and created BP functions. Each function hardly has 6-7 (or a bit more for some harder ones) execution nodes (commented and in order) so you wouldn’t say them cluttered.
There are several functions (not too many though) for every need. Not every function should have a use for everyone. For example there are several ways of adding items (using a placed actor, using an existing placeholder, etc) but in the example videos only one of them was used! I just tried to make the inventory in such a way so that anyone adding it to his project could find existing functions to recreate a gameplay element the way he intends to.
In case I wasn’t that clear I mean that if someone wants to add inventory items from the world only, he can use a function. If he only wants to loot corpses though (possibly a small inventory?), or trade with another character/NPC there’s a *different *already written function for moving stuff around!
To **conclude **with the first part of your question there are around 10-15 custom functions (where you should expect to only use a few of them) with only a few execution nodes in each!
Now for persistence, the marketplace restrictions still apply! If someday the marketplace allows code plugins I would surely have a try at adding db support!