I'm the CTO at inKind, a restaurant investment platform that allows restaurant owners to raise capital from their best customers.
I'm the CTO of a company, so I'll answer your original question.
One of the areas I'd love to see a SaaS product solution is reporting. Developers like myself often just focus on building the product and if they're smart, like yours truly, we add analytics.
But getting a clear picture of the business can still be difficult with different people on the team preferring different methods of communication. Some of our stats go out via email, and the people that like email only see part of the picture. All of our stats go over Slack, but not everyone likes Slack. I ended up building weekly email reports that totals everything up and gives the single, clear picture. Not every team has this capability though, and a single API to report significant events in the application with configurable communication methods for reporting and notifications would definitely be something worth paying for.
Along with other people in this thread, I'd definitely recommend talking to as many developers and companies as you can to identify real problems, rather than looking for one where it may not exist.
I hear this a lot and always say the same thing: if you can test your idea manually, without having to build any software, do it. There are so many great free software services out there nowadays and for most app ideas, you can string a couple services together or do part of it by hand to get everything going initially. Having real sales and usage will help you discover the things you couldn't have foreseen and understand your target user much better. Real sales/traction is also the best way to attract investors and technical co-founders.
The two option I would look into are using a gem called Paperclip, which provides the tools for uploads, url generation, and attachments as model attributes with any number of storage options, and using a service like Cloudinary. Cloudinary does the same things as paperclip, but is the hosting service for the uploads as well, which with images means they can do a bunch of cool stuff like color, size, and shape transformation on the fly. Cloudinary is a little more expensive though, so it's common for people to start with Paperclip and migrate to Cloudinary when the app grows.
Ruby on Rails is a framework written in the Ruby programming language for building best practice web applications. It's called "Ruby on Rails" because it follows the practice of convention over configuration - meaning that they make lots of small decisions about how you should organize your application to get you up and running quickly and with the industry best practices, as opposed to other frameworks that leave everything up to you to decide, which can be overwhelming when you really just care about the code that makes your app unique.
It really depends on what you're building here. If you can do any part of your product manually, I would suggest doing that in the first version.
The absolute fastest way is to hire a contractor to get it done, but that can be expensive. If your first prototype can't be built with a prototyping tool (even a Keynote presentation) and it's too expensive or difficult to build on your own, you have to convince other people that you are solving an important problem, that your solution solves that problem, and that you have the right team to do it. VCs in a seed round will care more about the team than the idea, but crowdfunders will care about both. And obviously getting designers or developers to join your team for equity will require convincing them of all 3.
Happy to give more specific advice based on your app thrugh a Clarity call!
I've created several MVPs for startup ideas, so I understand how to pair large ideas down into the most essential proof of concept and build it.
What's the main value add of your new social network? If the main value add is that it's a community specifically for a certain group of people, I would start by actually creating a community and getting those people involved in the community. If you can show that people actually use and value a community of specific people, that is way more compelling than just email signups of people that are interested in possibly leveraging a community that doesn't exist yet.
If I were you, I would use something like https://clubhouse.cc or Slack.com or Google Groups or Facebook groups to actually create a community and see whether or not it's a value add to your targeted users. Then when you prove that there are people leveraging the community and engaging, it's an easy sell to an investor that you just need money to build a custom app for your community, rather than a shot in the dark based on email signups.