That will depend on your nationality and previous entry history. Without that information no one can give an accurate answer.
If you’re from a country that allows for visa exempt then you probably won’t. If you’ve had copious previous entries prior to this year then you may well.
If it gets to that state then yes. Very very rare that it happens. But it could. Usually it’s the airline that has to foot the bill but it could be you that has to do it.
It only ever happens in fraction of cases. Probably less than 0.01% of times (a figure made up by me). Normal tourists need not worry. Someone with a “suspect” entry history may have issues.
It has happened in the past that someone with a valid visa has been denied entry but it would be an exceptional case were it to happen. And if so it’s probably because they’re on some form of Interpol or other list of persons unwanted in Thailand.
I don’t know your entry history but it’s super rare that someone would be questioned with a valid visa. It’s up to an individual immigration officer to determine whether to let you in or not so it’s impossible to say for sure.
The fact that you’ve never been asked is pretty irrelevant to the OPs question. Most people aren’t asked. Some are. If asked it needs to be in cash. 20k Thai baht or equivalent.
Very rare that a tourist visa would be denied as long as you supply the required documentation. Whether you need a tourist visa would be very subjective. Almost all don’t. And certainly isn’t going to help much if you have a questionable entry history.
IF asked to show amount (very few are asked) it would need to be 20,000 baht or equivalent in cash only. A bank account or credit card statement doesn’t suffice.
Cash amount is incredibly rarely asked for. The law exists that they can ask but they’ll only invoke the rule if they’re looking for a reason to deny you entry. For 99.9% of people that won’t happen.
Once you have the re-entry permit you can stay out of Thailand up until the date of your permitted to stay date. There is no time limit other than that.