Building another product

Hi folks,

It's been a couple of years since I tried to bootstrap something and posted it here.

I'm working on a visualization plugin for SketchUp pro, that I can hopefully port to other applications later. Although I didn't thoroughly validate my idea, SketchUp plugins seem like a pretty big market and there are already a lot of competing products out there.

The competition seems to be segregated into 2 ranges. Low-end visualization products target hobbyists, and high-end visualization products target professionals (architects, product designers, etc). I'm unable to compete on features with the high-end product but I'm confident that I initially can enter the lower-end market and build something better than the competitors.

I made an initial post on one of the Sketchup forums (link), and found 10 people interested in beta testing. I'm still a couple of weeks from beta testing, but I plan to generate some more excitement on that forum.

Attached is a work-in-progress screenshot.

I have a couple of questions for the wise sages on this forum:

How would I go about estimating how big my target market is? I see that the forum I posted on has ~1M users, my assumption is that 1% of that, 10,000 users would be potential customers but I might be wrong here.
I would love to use subscription pricing, but it seems that a lot of the competing products are selling one-off licenses. Is that a sustainable model, and would I even get away with trying to go for subscription prices?
I'm looking for a designer for icons for the application, where could I find someone without a lot of hassle? I had a couple of bad experiences in the past with Fiver, where anything more than 0$ would be paying too much for the work delivered. Would be great if that person also has experience with designing a look-and-feel for desktop applications.
What's an affordable tool to create a single landing page where people can sign-up for the beta program?

Cheers,
Thomas