Yes, we should definitely balance the internal and external linking on your website. There’s no set number of links for each but it’s always good practice to have some balance between the two and don’t go all-in on one over the other. If you are trying to improve internal linking on your website here’s a very good article about that: https://neilpatel.com/blog/commandments-of-internal-linking/
internal links are not very important for ranking but for having a low bounce rate and increasing PA. An important factor is also how much time your visitor spends on the page at your site. As it is already mentioned there is no number of how many internal links you need, nobody knows that. One thing you shouldn’t forget, making internal links on the same keyword, this can penalize you…google unfortunately hates this stuff.
On the part of external backlinks, it matters a lot what keyword you use. If you want to rank on the word “house rent London” you have to create backlinks on the same word. Don’t forget that even local SEO brings traffic and money, not everyone includes the city in a search. If you want to rank on local, you need backlinks to articles, when someone in the city of London just writes “house rent” without a cityGuest post -> Your Article -> Your Page