FTP very limited (chroot and r/o access needed)

I’m using Mikrotik RB951G-2HnD.

Is it possible to make root for ftp either per user or, if it’s too hard, adjustable in ftp configuration.
I’ve got USB HDD attached and I want users to use it for ftp, w/o possibility for them to access other areas like web cache or certificates.

Also is there a way to make some users to have only “download” access to ftp server, maybe via rights, f/ex. read+ftp = can only download from it, read+write+ftp = can both upload and download.

P.S.: If it’s impossible to get in release - is it possible to get sources and edit by myself? Can some1 toss me a link to required software or a HowTO?