the last date you can go is the date that's stamped in your passport. They already take a day off from the supposed 60, you don't need to do that yourself.
First of all, taxation goes by calendar year. It's therefore not directly related to an extension of your DTV. If for instance you arrived in 2024, you're not immediately at 180 days in 2025 when your initial 180 days run out.
Second, Thailand's taxation is progressive, percentages varying from 0% to 35% in 5 percent point increments.
Then, whether or not you bring money in or leave it elsewhere will not matter in the future. It was one of the weirdest taxation features that has ever existed, and luckily it is gonna go. If you owe tax over income or components of you income in Thailand, by the applicable dual tax treaty, you owe regardless of where you keep the money.
And then lastly, already brought up by many others: how things play out in your situation is very hard to tell without more info, and requires professional expertise. It's for instance quite possible that you owe tax in Thailand by some DTA even if you do not stay 180 days in Thailand. Or the reverse: that you stay longer but that your income is not taxed in Thailand. The 180 days limit only has marginal relevance and is given way too much attention. The most important implication of the 180 days is that you must report your taxable income if you surpass it, which could also be 0 if your entire income is taxed elsewhere by the applicable DTA. Best to consult an expert.
Oh, and last last: taxation is not handled by immigrations but by the revenue department.