1. You can try AWeb, IBrowse or the new OWB browsers. AWeb lite is included with OS3.9. IBrowse is available from
http://www.ibrowse-dev.net/ and you may find a flash plugin.
OWB can be found at
http://strohmayer.org/owb/. Flash is old and very basic
2.You need to install and configure the CD drivers supplied with AmigaOS 3.9 to use the uaescsi.device (enabled on Misc tab of Winuae).
3. Not sure if you can play DVDs on Amiga.
4. You need to configure Picasso96 and Screenmode preferences to use 16/32 bit colours using uaegfx driver.
FAQs at
http://www.pcguru.plus.com/uae_faq.html