What are the risks of using 301 redirects?

Question

Search Engine Optimization

Hello!
The site is based on one not very popular CMS, we plan to transfer it to our own system.
Naturally, page addresses [slightly, but] differ on CMS and self-written. As expected, in this case we will use 301, since it is not very difficult to do this for ALL pages of the site.
When using 301, assuming there are no errors and everything is redirected correctly, will it affect search indexing? Is there a risk of a drop in search traffic?
The HTML code on the issue on the CMS and self-written is almost the same, the only differences are:

1. OpenGraph markup will appear
   
2. A bunch of incomprehensible scripts that connected the CMS, but which were not needed, will disappear
   

With the exception of the above points, the page indexed earlier by the PS is identical to the one to which we are redirecting.
PS There are pages that are probably indexed, but as unnecessary, we decided to delete them altogether. Will the GENERAL positions be affected by the fact that a number of unnecessary (from our point of view), but indexed pages have been deleted? Will it affect other pages?
PS2. We do not change the domain.

Answer 1

Make better binding on pages (on the URI router).
Everywhere, specify the canonical tag for the new CMS so that the PS will blind the same content into 1 link. (for old ones - there will be two links: 1st - normal path, 2nd - old)
No 301.