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.
you are aware you must have the equivalent of bt800,000 in your home country personal bank account to get the type O visa. When you get here after you have your type O visa it is easy to get a Thai bank account, and I recommend getting two accounts at different banks. I have accounts with Bangkok Bank, and Kasikorn Bank. You'll see the advantages after you live here for a while. As long as you have enough in the accounts to cover the yearly service fees nothing happens to the accounts no matter where you are in the world. When you actually decide to move here it is much better to do a SWIFT transfer of the bt800,000 all at once rather than small transfers over time. By doing it this way you can get a FET, foreign exchange transfer, document if you ever decide to leave Thailand and want to send the whole amount out of Thailand. You'll need the FET to justify where that much money came from, meeting anti money laundering laws Thailand enforces.
you can apply from the Philippines no problem. One thing document wise they ask for now in cases like yours, with no legal business, is your most recent income tax return. If you are rejected the fee is not returned. It is lost, and a new fee is required to apply again.
there are no rules saying you must attend classes. The only rules that have been added are for the one in country extension, which requires all the original documents you used, and updated. Those are the only rules that apply after you have the DTV. There are no rules, or requirements, when you exit and come back. You don't even have to prove the money is still in your bank account.