App Engine: Few big scripts or many small ones?
The are two important considerations here.

The number of roundtrip calls from the client to the server.

One call to update a user profile will execute much faster than 5 calls to update different parts of user profile as you save on roundtrip time between the client and the server and between the server and the datastore.

Write costs.

If you update 5 properties in a user profile and save it, and then update 5 other properties and save it, etc., your writing costs will be much higher because every update incurs writing costs, including updates on all indexed properties - even those you did not change.
Instead of creating a huge user profile with 50 properties, it may be better to keep properties that rarely change (name, gender, date of birth, etc.) in one entity, and separate other properties into a different entity or entities. This way you can reduce your writing costs, but also reduce the payload (no need to move all 50 properties back and forth unless they are needed), and simplify your application logic (i.e. if a user only updates an address, there is no need to update the entire user profile).
I am working on a website that I want to host on App Engine. My App Engine scripts are written in Python. Now let's say you could register on my website and have a user profile. Now, the user Profile is kind of extensive and has more than 50 different ndb properties (just for the sake of an example).
If the user wants to edit his records (which he can to some extend) he may do so through my website send a request to the app engine backend.
The way the profile is section, often about 5 to 10 properties fall into a small subsection or container of the page. On the server side I would have multiple small scripts to handle editing small sections of the whole Profile. For example one script would update "adress information", another one would update "interests" and an "about me" text. This way I end up with 5 scripts or so. The advantage is that each script is easy to maintain and only does one specific thing. But I don't know if something like this is smart performance wise. Because if I maintain this habbit for the rest of the page I'll probably end up with about 100 or more different .py scripts and a very big app.yaml and I have no idea how efficiently they are cached on the google servers.
So tl;dr:
Are many small backend scripts to perform small tasks on my App Engine backend a good idea or should I use few scripts which can handle a whole array of different tasks?