Host has switched to fcgi
FastCGI should be fine, however...

Your .htaccess may be replaced each time you upgrade Drupal, depending on how you upgrade files.  If you do it manually, you need to diff the new one with old one, and determine if there are any changes and merge the changes.

In actually think all of those settings should be the defaults now in the stock PHP php.ini-dist, but I am not positive about the mbstring ones.

It is very probable that your permissions of your files directory (eg, sites/default/files) is messed up.  Double check that Drupal can read, write, add, and remove files.  The status page should show any problems, but you need to test all cases.

But, one common configuration with FastCGI with shared accounts is that Apache runs as your account user.  This would mean that the site files and the files directory would be owned by the same user.  This is a security consideration to keep in mind.  Preferably, the site files should not have write access by the webserver; write access should be as limited as possible.  You can "solve" this be revoking write access from your user account (ie, make files 444 and dirs 555) except for sites/default/files, but this is a major hassle.

If a host did that to me, I would be EXTREMELY upset.  The provider should have warned you ahead of time so you could prepare, and also given you a test account so you could properly test things out.

Personally, I always recommend true VPS accounts to clients who want to run Drupal.  The only time I would consider shared hosting are cases where the provider specializes in shared Drupal hosting.