Does "Development principles" also include transparency of teams' plans when it comes to findability of such plans (links/documentation) via wiki pages? Or is that out of scope?
As I've been looking at team homepages on mw.org (can I quickly find out how planning is done and how I could get involved?) and whether teams listed their quarterly goals. Results are mixed. I'm happy to help somehow™.

This is a basic list of 7-10 principles that engineering teams commit to following. Examples we looked at are Unicef's and gov.uk, and of course, are not prescriptive.

"Transparency" may very well be one of the principles we end up with - I mean, it would be quite strange (and would be noted) if it did not end up on the list.

Product Process (step by step and tools) is much more involved, and is a different project.

I've said something (a bit) like this elsewhere but for the record - I'm hoping that this will make absolutely clear the need for the ability to integrate volunteer developers across all foundation-initiated development projects.

Even, for example, where few of those projects may need to be private (security, some operations stuff, etc.), trusted volunteer access must be possible.

Are the "7-10 most important principles" this task aims to define the same as the "10 tips" from T113490: 10 tips for communicating with communities when developing software?

If they are, then this task is in practice a blocker of the other one.

Not at all the same, and no blockers between the two.

Principles are the principles that product and engineering teams bring to creating software in all of it's capacities. Tips for communicating are more tactical around communication skills, locations etc. These principles will be made in collaboration with all of the product and engineering teams throughout the Foundation. T113490 is about engaging and collaborating with users.