But is there a way to do what I want with excluding pictures/ at first.
Yes, that's straightforward. WP is built around mod_rewrite. So everything you need to add should go in your htaccess immediately
before the WP section (the part that begins and ends in #comment lines).
The RewriteRule that creates your redirect will need a preceding condition that says something like
RewriteCond %{REQUEST_URI} !/pictures/
without anchor.
Also is there a way I can redirect without the capitalisation in the old URLs or will that not matter as the new page lowercase?
This part is trickier. There is undoubtedly something in WP that changes casing, and maybe also something that replaces _ lowline with - hyphen. You may need to add a plugin or check a box somewhere; see the WP subforum for details. But that's a pretty server-intensive approach.
Since it isn't your own server, you do not have the option of using Apache's built-in case-changing RewriteMap function. (That is: you
probably can't do it. You can use a RewriteMap in htaccess-- but only if it has been defined in the config file. Your host probably hasn't taken this extra step, because why would they. Mine doesn't; I asked once.)
That leaves two other routes.
One option is to rewrite (not redirect) to a php script that does all the replacing and case-changing in one fell swoop and issues a redirect at the end. Now, you did say you formerly had a hand-rolled CMS. This means that possibly somebody in your organization speaks php, and they could run up such a php script in about five minutes. (That is, about five programming minutes, translating to no more than an hour as measured on the clock.)
The second option is to make a whole bunch of RewriteRules, one for each letter of the alphabet, and string them together with [N] flags (omitting [L]). I do not recommend this approach unless your name is J.D. Morgan. Even the Apache docs say
Use with extreme caution
