How to safely change the URL system on the site?

Question

Search engines

The site is completely moving to a new CNC system, it has about 6,000 pages. It is necessary to put 301 redirects from all old addresses to new ones. Question 2:

1. Will the server kill a 6000 line htaccess file?
2. Will search engines normally perceive such a transition?

Perhaps there are some better ways to do this?

Answer 1

Won't the server kill a 6000 line htaccess file?

Should not, if you do not have some kind of completely crazy load.

Will search engines accept such a transition normally?

Should be taken well. Check out their URL migration guides, I haven't read them for a long time, maybe something else can (or should) be done in Webmaster Tools and similar places.

Perhaps there are some better ways to do this?

You can also make redirects at the PHP level (or another language in which the site scripts work), especially if the static remains in place.
Also add a rel canonical tag to the head for new addresses after the system update.