Having collected over 70 ideas, it was not obvious which we would build first. Especially, since we didn't know all the details of all the ideas when the other just wrote down the name or a rough description.
Also, we had very different gut feelings about what constitutes a "good idea". Our interest in the different stacks also differed.

Going through the first batch of ideas, explaining them to each other and trying to rate them consistently, it became clear we would be there a while.
We took a few steps back and started with our rating rubric. We defined 5 areas and assigned a value from 1 to 5 to each of them, with 5 being the best and 1 being the worst.

Financial potential

What kind of MRR can we expect?

1. no monetization potential

2. 0 to 200 bucks per month

3. 200 to 2k bucks per month

4. 2k to 4k bucks per month

5. over 4k bucks per month

Feasibility

How long does it take to build?

1. not feasible for us at all

2. over a month

3. 2 to 3 weeks

4. 1 to 2 weeks

5. under a week

Automation potential

1. every purchase requires repeated effort

2. every customer requires effort for onboarding in addition to constant content management and creation

3. no customer onboarding, but constant content management and creation

4. no customer onboarding, but some manual effort on occasion, like support rare requests

5. no product content management and no customer onboarding

User-generated content independence

How much of the value is based on user-generated content?

1. the whole product value is based on user-generated content

2. the ratio of independence to user-generated content is 25 / 75

3. the ratio of independence to user-generated content is 50 / 50

4. the ratio of independence to user-generated content is 75 / 25

5. the product value is not based on user-generated content at all

Marketing potential

1. the niche is difficult to define and hard to capture

2. the in-between state, as defined by a gut feeling

3. the niche is neither difficult nor simple to define and neither hard nor easy to capture

4. the in-between state, as defined by a gut feeling

5. the niche is easily defined and easy to capture

Not all the values were easy to associate with real word representations, especially with low to non-experience launching a bootstrapped startup. Finding a common rating rubric, that we both agreed on and would result in the same values if rated by either of us.

It took us an entire day to go through all of them, getting sidetracked often while getting into heated discussions by our enthusiasm for an idea or an argument about whether we want to pursue something.
Keeping each other accountable to only spend a few minutes on each rating, disregarding our drive for perfectionism, helped immensely.

At the end of the day, we had a few ideas with an average score of over 3 or even 4. Most of them relied on Cloudflare Workers, making them mostly easy to build, low cost, extremely scalable and easy to install.
They would be the first ideas we would build.