Generally you just need the funds in your account at date shown as an international transfer, unless you apply at Jomtien immigration. For the extension of stay you’ll need two months seasoning.
You’ll get another 60 days upon your return and you will probably be able to get two 60 days visa exemptions if you don’t do any 30 days additional extension and you can prove onward tickets. But things have become quite strict now. The safest option is always to get a multiple entries visa if you’re going to do several entries within a short periode of time. A six months multiple entries tourist visa will easily secure your whole trip with a visa. The decision is yours to take.
As a US citizen you’re entitled to a 60 days visa exemption upon arrival and in the discretion of the IO you meet in the immigration. You can’t get a re-entry permit on a visa exemption, so technically you’ll get two 60 days visa exemptions. If you prove a ticket out of Thailand within 14 days when returning from the Philippines you should be fine with this without applying for any visa.
I have three bank accounts in Thailand opened myself for several years, but you obviously don’t know the situation and catch 22 people are struggling with now regarding bank accounts and visas/long term stay in Thailand.