Hi Luke
For sure, carving away 2/3rds of your previous site is a big chunk, but I don't think that should overly concern you.
If you had said you were thinking of doing this a couple of years ago, I would have encouraged you to think again on the basis that the more pages your site had, the more weight it had, the more pages could be optimised and the more entry points there were from search.
With changes in recent months to Google search, in particular the move to semantic search and away from Boolean search, then having a keyword rich site, with many well optimised correct keyword density pages, shouldn't be the focus any more.
I'm not suggesting that having 35 pages compared to 107 pages is better. What I am saying is that it is better to have 35 sharply focused, high quality pages than 107 pages that don't have the same definition and focus. The measure should most definitely be quality over quantity, both on a page count basis and even on a word count basis.
What I would focus on with your 35 pages is making sure they are well structured (so many on-page SEO rules still apply - so make sure the faulty parts you mentioned are fixed) and the navigation is clear.
I am sure you know this, but make sure that your pages are customer-focused, so that they answer the type of questions your customers are asking in the language of your customer, and where related questions could occur, make sure there are good internal links between related content pages.
Finally, when you do the switch, I would just make sure that you think about your 301 redirects. Where an old page no longer exists on the new site, then redirect it to the closest related page.
I hope that helps,
Peter