How can I extend my stay in Thailand using a tourist visa or by transitioning to an ED visa?

Hi all. I entered Thailand last month having applied for a 60-day tourist visa, but as it came through two days too late, wound up entering on a visa exemption, with a 30-day stamp that is good through this coming Saturday.

Tomorrow (er, well, later today), I'm visiting Chiang Mai immigration to — I think, unless someone suggests otherwise! — apply for a 30-day extension for tourism.

I still have, or have access to, that 60-day tourism visa that's ready and waiting, but I believe I would have to leave the country and re-enter using that for it to come into play, correct? (What would be simplest in my uneducated-on-the-topic view, is to just "switch" to that now, but that seems impossible?)

(The end goal here is staying another three months or more; more on that below.)

I've read all about what I need to take with me for the 30-day extension and have all that ready. I have a few questions, though, if someone with experience would be so kind as to answer:

* First, should I tell the immigration officer about the already-approved 60-day tourist visa? Will she/he see that in the system somewhere regardless? Mostly I just don't want to look shady by asking for one thing when I already have another one.

* I have two TM-30 forms now, because of timing of my many moving parts: One for the hotel I've been staying in, for which I've paid through Saturday. And now having signed a three-month lease on a condo here, I also have that one from the landlord. Should I present both and explain? Should I just hand over the hotel one, which seems like it would raise fewer questions? Or the longer one?

* I had booked a flight to Singapore leaving on Saturday thinking I'd need to show that on arrival at the airport last month, but was never asked for it. Should I either take proof of that to the immigration office and/or reschedule it for a day that is 30, 60 or 90 days in the future?

Sometime in the next couple of months, I'm planning to transition to an ED visa — a legit one, as I'd like to start learning the language and also attend the lecture series at Chiang Mai University. I don't think this is particularly relevant to my more immediate query, but mentioning it here just in case it's more relevant than I realize. (I think I've ready that prior to pandemic-times, you had to be on a TR visa, rather than just an exemption/extension, to make that change in-country. But if I'm reading correctly those rules seem to have been relaxed now?)

Many, many thanks in advance for your help; and for letting me into this knowledge-base!