I've launched a new website which is essentially a search engine for a large amount of data.
It sounds like you're trying to re-invent google. This is a bad idea. No one wants to go on a search engine to search for a website which functions as another search engine.
The website has a homepage with some content and a search box. Search results aren't indexed, and each result has it's own standalone webpage (70k pages).
I suggest adding more creativity and not making searching a requirement in your site. Make your site more natural and interesting to guests.
The problem is that each page is very light in terms of content, probably too light to warrant finding a way to index them (via sitemap), as it could do more damage that good.
If you want, you can register your domain name with Google Search Console and check your sitemap status to see how many pages are indexed. I'm going to predict the number of indexed pages won't be in your favor due to very little content per page.
So there's two questions, really: Should I (attempt to) index the 70k pages? Each page just contains a data table.
Search engines are able to index quality pages. There's no sense in you attempting to index the 70k pages because search result pages aren't interesting pages people want to view. When I click a link in google search results, I want to see an interesting page with text and maybe graphics, not just a page showing more random search results. Just a data table might not be enough to qualify as a decent page to index unless there's quality and descriptive data in it with a heading and a paragraph or two above the table that describes it.
If not, how would I rank this site as it only has one page otherwise (homepage)?
If you really want to index the site, start with the homepage and create a document containing at least 200 words and optionally add images. Follow SEO tactics and test your page against multiple free SEO tools on the internet. Once you done that, then google just might index your page automatically.