Having the database on a different system obviously increases the latency of any database access a little, but in my experience this does not significantly alter the response speed of my websites. Having said this, I do not operate any forum sites, so I can't comment on how these might be affected.
I am not sure about direct bank transfer or Western Union, but the following payment types are shown in the DreamHost panel...
Check or Money Order
I should note that there are some restrictions with regard to PayPal and the use of promo-codes.
Another option, if you do not have a credit card, is a direct debit card. I have a VISA direct debit card from my bank and I find it is accepted by most places that require a credit card.
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