While submerging the pot is good habit
I understand your point, but if you must submerge the pot to get water to the roots, you need to consider repotting so you can water properly.
this type of bonsai is not suitable to be kept indoors at all
Incorrect. keep it indoors (at least for winter)
Not completely correct. This tree is semi-deciduous and adapts to various climates. In general it is better to keep trees outside. In the Netherlands, in our current winter, that would be no problem at all (though it seems we're going to get colder weather). Things are different if the plant has been kept indoors, temperatures outside are dropping, and it hasn't hardened off in autumn.
Do NOT feed it in winter
Not entirely true and conflicting with your earlier advice. When kept indoors, you can feed it (if needed). Bonsai4me says once monthly:
www.bonsai4me.com/SpeciesGuide/Ulmus.html
It doesn't at all appear as if you have done any research. Next time maybe look around on this website a bit before asking questions?
That I fully agree with.
It's not like he's the first person that has a new bonsai. This forum is flooded with it, with the same, S-shaped, ugly, commercial, cheap, wannabe-bonsai type of plants. Likewise, the same questions are asked over and over and over again. All the information is available, under the Basics at this website, and in the forum, where these same questions have been answered many, many times.
If you have not seen that, you've not done any research and you're just being lazy.