Box does throttle uploads, but it is rate, not number. Box throttles 4 files/sec.
What is the upload method? Web? FTP? Box Sync? Box Drive? WebDav?
I don't believe Java is part of the web upload anymore.
Chrome. FireFox. Safari. Opera. All work fine.
Friends don't let friends use IE.
You should be able to download the entire folder, not just what's on the page. If you click the [...] (more options) for the folder, you should see this dropdown. Select "Download" and it'll give you the entire thing in one .zip file.
Alternatively, if you're already inside the folder, click the folder name on the folder path (on the top), you'll get the same dropdown with same options.
Excellent tip, @gordio283. NOTE: If the total size of the download is over 15GB it will not download the whole thing and it will not tell you it is incomplete.