I would say so, I think Zelda has enough fans on Switch by now that it should be quite doable. If TotK sold 10 mil in three days then I could see this doing 3-4 mil (we'll get a decent idea of that since it's at the end of a quarter), and then there's the holiday right after that which should add a couple more very quickly.

Definitely possible.
Not guaranteed, but would not be shocking.

large install base, sure, but also heavy over-saturation of first-party exclusives. There’s a reason why titles such as SSBU, BotW/TotK, SMOdyssey, etc., are struggling to even hit 500k each quarter, whereas in the past they would easily sweep million(s).

While I agree with you I think there's other factors at play here as well. 

I think this game will sell very well

Its not a hard bar to clear considering the install base of the Switch, so its likely it will.

If it does pass the original LoZ it will not be an amazing achievement given the size of the market today as opposed to back then. Unless it passes the LoZ by a large amount and moves significant hardware, I don’t expect it to do either.

I don't think Echoes of Wisdom is going to sell more than Link's Awakening. Sure it's a new game vs a remake but it's the second Zelda with the same style on the Switch, and second Zelda games on the same system always sell less than their predecessors.

if the game is good, yes

I'd argue due to the size of the install base and the appetite overall I've seen for it since it revealed mechanics that are reminiscent of BOTW/TOTK, achieving 5M copies sold during the first quarter + Holiday season is doable. I don't know if it'll have good legs due to the overcrowded market presence of 1st party games on Switch at this point, but it'll do good.