The number of directives definitely impacts webserver performance and thus page load time. As you noted, performance-wise, placing such directives in the httpd.conf is preferred since those directives are parsed one time while .htaccess directives are processed for every request to that directory or a child item within a subdirectory.
The performance difference is usually negligible (milliseconds) for many small websites. However, if your site has a lot of traffic, or for that matter, is on a shared webserver with several other sites which aggregate to heavy usage/volume, then the performance degradation can definitely be more observable.
There's no defined "recommended number" of directives, but a good rule of thumb for a shared hosting environment is to only add the directives you absolutely need to .htaccess. Your hosting provider's cpanel may often include webserver application configuration options at the httpd.conf level for things like:
- Type Handlers
- Cache Expiration
- Permissions (directory listings)
- Compression
This post also discusses more about performance considerations: https://stackoverflow.com/questions/25063677/how-much-does-using-htaccess-files-slow-down-website-performance-especially-wit