Should I do a 301 redirect if I'm going to do regionalization?

Question

Search Engine Optimization

The site used to have a product with the name site/tovari/12345, later the names of the cards were renamed to the full value site/tovari/product-mashina-megaspeed . The site is young, there is practically no organic content, but advertising brings 20-50 visitors a day. It was decided to ban them in robots and remove them manually from the Yandex webmaster. As a result, a lot of unnecessary forbidden urls appeared in robots on old pages, then we remove the prohibition of crawling through robots from old pages and within a month they reappear with a 404 error, although they are not in the sitemap.

After that, there was a problem with the site and in order for everything to be automated, it was required that all products be with a slash at the end (previously they were without a slash). Don't ask why the slash situation was needed, it doesn't matter now. As a result, at the moment there was already organic traffic and I didn’t want to lose it, we redirected the old url + without the url slash to a new working valid url address. It turns out now that 2 old urls refer to the current url. As a result, positions sank in indexing.

Please answer a few questions:
1. Is it possible to permanently remove a 404 page from webmasters - so that it does not pop up anywhere else?
2. What to do with 2 urls that now link to the valid url (now more than 2000 redirects). Is there a 301 redirect for some time - after which you can no longer refer to a valid page with a 301 redirect and just remove the redirect and try to remove it manually from the webmasters?
3. If all the old urls get the value - "the canonical url is the current and current page". Maybe you should just wait and everything will work out with the positions?
4. I plan to add regionality and I assume that all this mess with 301 redirects will make me problems with regions and thousands of people will start chaos with 404 and 301 redirects. Reset it all and send a sitemap with valid urls and it's okay to do regionalization.

Answer 1

To be honest, the person who did all this is called in nature an asshole, I apologize for the expression, pay three kopecks and hire a SEO specialist who will tell you how to do it whole, and not five improving actions that contradict each other and which you came up with.