Search 'issa compass' on Google Maps and check their reviews. For about 5k thb, they ensure you get your DTV (or money-back) and prepare everything for you. It usually takes less than a week (less than 4 days in Vietnam for mine). Good luck with yours!
Hanoi was great for me, just 2 weeks ago, got my visa (soft route) very quickly, in less than 4 days. If, for any reason, you're not sure about going the workation way, simply go for some Muay Thai or Thai Cooking. It can be a good experience and you'll have no problem getting your DTV. Just make SURE you have those required 500K THB (or equivalent) on your account for AT LEAST 3 MONTHS. Good luck and see you soon in Thailand!
I didn't have one during my initial 2 years in the country and it was a pain, in my opinion. Having one later made everything just much easier and smoother. But of course, everyone has different needs.
Cash is king? Well, in Thailand, most transactions are done using QR codes these days. I wouldn't want to be carrying cash on me everytime I need to go somewhere. However, I always have my phone with me, like most people here. Having a bank account is so much more convenient, and even if you can certainly survive without one, I wouldn't want to stay here for years with cash only for every transaction. But I'm glad it's apparently not a problem for you.