Feedback on ideas

I am a developer and have been working full time most of my life. I don't dream of making a multi-million dollar startup. I'd like to start with sometime basic and small just to see how things go.

I am not really big on talking to people and collaboration outside code/architecture, because of that getting feedback on ideas by talking to real people is a bit of an issue for me(given I am a introvert), I've decided to all ideas that I have here, and let everyone give feedback. This exercise is meant to serve 2 things for me:

1. Break the ice in terms of talking to people.
2. Get feedback on where I am (all these are more likely than not horrible ideas, but it'll be good to get some feedback).

List of ideas:
Rebuilding something that already exists:

1. An API/web page monitoring tool - Kinda like uptime robot, but also add the ability to track APIs and create monitors programmatically.
2. E-commerce store push notification system - Something like push owl, the same set of features but a different pricing model?

Originalish Ideas:

1. API platform for scheduling API call backs.
2. Plaform for helping individual developer turned founders with marketing.
3. Platform for running LinkedIn connection drip campaigns.
4. A community feed for shopify stores.

Are these even doable? Assuming I want do some market research, how do I reach out to potential customers without putting a lot of effort into making the product? Do I just create a landing page and then email people about the product I am trying to make? or Do I make an MVP or something which is minimally demoable before reaching out to potential customers?

Thank you.