This is a tough but common problem. In the perfect world, you'd hire a team of high quality content writers on a contract to populate each of these pages with genuine, unique content.
Since this isn't the perfect world, you're probably on a budget that doesn't allow this to happen. Assuming your site is already live, that means you no longer have to deal with the "push it live with sparse pages or spend a few more months preparing properly" conundrum.
That being the case, my suggestion here is always to just do it properly and it takes however long it takes. Assuming you've had the site up like this for some time, your rankings are unlikely to drop in the next month or so. Start populating content from the top down, namely from your primary landing pages to your category pages, subcategory pages then finally the individual products.
In my experience, ~300-500 words seems to be sufficient for a product page so you may be able to stretch that budget with a good writer to maybe 4 or 5 pages, maybe. It's more about offering value that an arbitrary word count anyhow.
You could always get them to do the first few and you follow their lead from there, perhaps getting them to proof-read the first 10 descriptions that you write? Not ideal and I'd only attempt this if your writing abilities are ok (they seem to be?). If you're going to go this route, I'd suggest using Grammarly to keep an eye on your spelling and grammar for you as well - it can integrate with Word if that's your tool of choice or you can type straight into their web app.
Anyhow, back on topic, doing it this way means your most valuable/sold/profitable products will be getting content first and you're not compromising on quality. We've done exactly this with a number of medium sized ecommerce sites and the results are always great (albeit in conjunction with other work we're doing). Naturally, the faster the better but you have to start somewhere.
There was a Whiteboard Friday on this exact topic and I think I just found it but the video is broken and it was old so they don't have the transcript The closest I could find was this one which is also quite old but worth watching. Don't forget that Google's intention is to ignore duplicated content so if you're just copying from other sites, there's a good chance you just won't rank with those pages.
Hope that helps!