The investment visa is through the BOI, board of investment, and all investments, and condo purchases, must be approved by them. There is also an extensive background investigation that takes about three months.
It's mostly to take advantage of those not smart enough to do it themselves, at half the cost. There is no requirement to stay out of the country like most want for a visa exempt entry return. With the DTV you can cross any border, or fly anywhere, and immediately return, with the only wait being how long the queue is. Most use the border bounce vans so they can continue doing visa exempt entries, and not get rejected doing it themselves. You don't have that problem, for five years.
I use one bank for all my online purchasing. Thailand uses lots of e-commerce now. One of the other one's I use for all my living expenses. I have 4 accounts at two different banks.
I use one for online purchasing, to keep that separate, as lots of e-commerce in Thailand now. As far as immigration goes, and I'm in Bangkok, I just do a transfer of a few baht from one bank to the other that morning I extend, and update my bank book in the machine. It makes that requirement real easy with two accounts.