Ask HN: System-design Aspects a good Blockchain engineer should know

Folks who are working on blockchain- Ethereum, hyperledger, Ripple etc -

For Engineers who understand what a blockchain is - Merkle tree, Proof of Work etc- what are the "meta" things about the domain, I should know, to be an effective engineer, system-design wise?

For instance:

1)On what metrics should a developer decide whether to go for Ethereum vs Hyperledge? Both technical and non-technical ( community support/ stability etc)

2)Should I be designing my application that it is agnostic about underlying blockchain? If not, how?

3)What legal rammifications could be there in using Blockchain to store hashed dataset for integrity validation? ( Eg GDPR)

4)What are some common 'metrics' which would distinguish a two 'Blockchain applications' which do the same exact thing? ie- if I were to compare two photosharing service (like instagram) - then the obvious metrics could be (1) Time to upload images (2) Time to search images

5) Microservices vs mult-layered app : Pros vs cons

6) Potential Upgrade scenarios & Pitfalls

7) Design issues when trying to implement a multi-tenant services using blockchain. Example: Lets say I have a service - "use blockchain for X", and I am designing this for an organization level.

8)What questions should I be asking about system-design?