You mean like Flash or JS games? If so, then yes you should have no problems running these on your site(s).
Yes, you just need to specify a different root directory (and/or domain) and database for each install.
You will be unable to pay for your hosting using PayPal if you use a promo-code. Also, I don't believe you can merge accounts if one of them was created using a promo-code (at least until the initial plan period has expired).
These are the only disadvantages I can think of.
Both VI and Pico are available through SSH, I am not sure about any others.
I don't believe this is possible. However, you can host as many domains or sub-domains as you like under the one plan, but they will all be on port 80.
Yes. It is easier to create a sub-domain and give the user access to that, but with directory mapping you should be able to achieve what you want. You can also set separate disk quotas for all machine/ftp users.
The difficulty of transferring the domain will be determined by godaddy, there is not much you need to do on the DreamHost end. The alternative is to leave the registration at godaddy and host the site at DreamHost. You can do this by simply changing the nameservers over.
There shouldn't be, but the downtime varies, depending on how quickly things propagate around the Internet.
If you fully transfer the domain to DreamHost, I imagine you will have to reconfigure your email forwarding using the Web Panel, this should be a relatively painless experience.
No problem, glad to help.
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