I'm on the same pre-superlemon journey. Similar background, eg need tech co-founder, ex-SPM at high-scale & successful products (XYZ, ABC (redacted)).

Questions (note: i've read all your blogs already):

Q1. If having daily full hours, total time I will take to find the right shopify biz-idea? (in build OR buy model. hence existing biz to grow, OR for new biz to start)

You have a mindset problem. You're somehow looking for a definite answer "total time I'll take to find a biz-idea" for a journey that is completely full of uncertainty.

The answer? You could find your biz-idea in 1 hour, or you might not find it after 100.

The real question is - How much time have you already spent trying to do your research? If it's less than 10 hours, then why are you wasting time talking to me.

Q2. Businesses to consider if certain that I'm on a 10+ year online-biz journey, BUT I need $3K+ MRR by Month 5 of launch. I will not start this journey if year 1 cannot achieve this.

Same answer. If you won't start because you want a guaranteed result, then perhaps business is not for you. Perhaps you're used to "do X for Y hours, and Z result is guaranteed."

If that's your mindset, I am sorry but this path will be painful for you.

However, if you're willing to change your mindset, then you will start asking the right questions.

Right questions:

1. Have I discovered a problem that people really face and are willing to pay for?
2. Have I figured out how to reach the first 10 or 100 such customers?
3. Can I hustle and figure out all the nitty gritties as I execute on points 1 & 2?

Now ask yourself - How much time have you spent doing 1 or 2?

Q3. What should be my 10 yr horizon planning safety nets? before starting this journey, so I know my exit costs. eg tech investments done, tech co-founders, etc

Plan to get your first 10 users.

Your 10 year plans are going to change. Your 1 year plan is going to change. None of those plans matter if you can't find your first 10 users.