Fonts: If you install a font on your system, it will appear in the Text filter’s font options. If you are looking for a pixel font you might want to check out the links in this recent thread: Sauron’s Video Title - great work!
File size: Shotcut is definitely able to handle large files. My first guess is that your source video has a variable framerate, which is notorious for causing problems with Shotcut. Can you give us any details about the source files?
Exporting: Shotcut is definitely capable of exporting at full hd. Can you give more details about not being able to export? Is it crashing, or do you not see other export options, or…?
Please also consider this post when asking for help, as the more specific information that you share the better people on the forum can help you: Requesting Support