Be prepared a lot of people will not sign an NDA.
Reasons include:

- they have multiple interests, and may already have something similar, or may identify someone who can execute in the future; an NDA prevents them from pursuing this in the future or possibly moving ahead on current developments

- you need them more than they need you; you have no leverage, that's why you're asking for their help.

It sounds like you are not looking for a technical expert, you're looking for a business expert.
Consider:
- customers are your experts that provide feedback on feasibility;
have you launched a minimum viable product to obtain feedback through?

I highly recommend learning lean startup methods and evaluating whether they offer a better route. They will help you learn regardless of who you discuss with, and
it may be easier & faster to engage experts *who will USE the product
than those who will have an opinion on the product.

- Produce content of value to potential renters about their area/s of interest, and distribute using the free platforms available. This will help build brand.

- Produce content to educate renters about the equipment, how to use, how to repair, how to service, so they can see how easy it is. (Distribute using the free platforms)

- Produce content to educate renters on better construction practices, so they can improve their business. Creating value this way both builds brand and grows your customers business

Contact multiple orchestra's.
I know one in southern Ontario has already taken their performances online;
if your proposed vision is enticing and benefits them you might be able to collaborate with several orchestra's for a performance.
Why do you want 1000 participants?

Start experimenting by putting the 2 things in place you say you are missing:
1. create a validated learning model
2. Stop focusing on vanity metrics; replace with user growth, cohort analysis or growth metrics.

Do not just read Lean principles; APPLY them.

Also,
What are you doing to brand your company?
What are you doing to engaging people who have the problem your service solves?
Does it actually solve their problem? Do you know what their problems are? What do THEY think their problems are?

Do you actually mean Lean Product and Process Development?
If so, great examples you can find are:
Toyota, Goodyear, Harley Davidson, Ping, Ford, and recently I notice TechnipFMC Schilling Robotics.

You can also find articles on companies that haven't adopted this as a business strategy yet have had success applying it in a specific product development effort, such as Metso Neles NDX intelligent valve controller.

If you're building in China, your IP isn't protected. You also incur travel costs, long transit times, quality issues that increase product development time, Chinese New Year shut down (for weeks), etc. and the wage gap between the US & China is closing. A lot of 'leading' companies do not fully understand the real cost of offshoring. Search 'Reshoring Initiative TCO' and use the total cost of ownership calculator. Cost is not the only reason, product development is also a factor. There's a reason why Toyota moves to local markets. It's the same reason many Chinese companies move to the US.

Not in the last 14 companies, or any of the start-ups, have we had a need to purchase any so called 'lean software'. A lot of companies are selling the idea 'our software makes you lean' - it doesn't - the CEO drives lean. I've yet to come across a vendor charging for something you can't do without them in house at little to no cost. Try a whiteboard

You 'know' it is content driven, user based, and simplifying feeds this. You assume investors are needed. Why do you think it will not generate revenue? How does it make money? Try to prove your concept will fail and you may not need to ask them. Read the Lean Start-Up

Yes, in order to explain your idea a model will be helpful, which you can also take photos of to support your description online.
Consider using drone parts to build a cheap small scale functioning prototype.
Drawings can help, whether engineering or illustrations (what ever is cheaper to start) and support your description online.
Understand the trade off involved for VC money - how much equity and control you are willing to lose in exchange for this.
Figure out how much money would be required, even if only estimating the parts list at first, and what you need to be selling to determine if it's a potentially profitable venture before spending time on it.
How much are cargo drones costing? What can you learn from these?
How can you validate whether you've identified a buying market for this?

Read 'Venture Deals 2nd Ed' by Feld to prepare - pound through it over a week if you're tight for time. A pdf is available online if you can't get the paper copy.