For い adjectives you forget to mention that you have to switch the い for く。

I can see the "remove" under the "i", but I misread it too at first. Maybe there is a way to make the "remove" more prominent? Maybe by putting it in a box or something like that. If you don't know you have to look for something, it's easy to miss.

Ok, making the remove marker more obvious. Will go into the next update. Thanks for pointing out the bugs on the construction table. It's all automatically generated, so it's still a tad buggy.

Thanks - took it out of the list.

That is used for making something polite/keigo; You use it to describe the actions of others above you.
http://www.renshuu.org/index.php?page=grammar/individual&id=140

I sent a correction suggestion, but the model sentence ending 「～歌手になりたかっただ」strikes me as unnatural. How about ～なりたかったです。 Or, if this were an explanatory sentence ("When I was a kid, I wanted to become a singer, so I have always loved karaoke", etc.) ～なりたかったのです　or なりたかったんです

When you want to say that things became a certain way, but you're not talking about a time-specific event ('I became sad when my dog died') but a state of being that happened but is still ongoing, do you need to use a -ています form with it, too? My sentence was: 隣のお爺さんはさびしくなった. But I'm wondering if I'd need to express that kind of thing (basically, present perfect in English) with something like 隣のお爺さんはさびしくなっていました。

Yes, that makes sense, thank you! (And I'm pleased I don't have to remember to Lego another word on with that construction. :D )

As mentioned by the previous poster, I also came across such usage and was wondering how to use it.

I found this note in "Introduction to Japanese":

「

While typically used in combination with the verb particle に, なる can also be used in combination with the particle と (not in its role as noun lister), in which case its meaning changes from "become" to "be" (often interpreted as the immediate future "will be"). This can be illustrated with some に/と comparison sentences:

• 力になります。 "(This) will become (our) strength".
• 力となります。 "(This) will be (our) strength". (...)

」

Has someone a more detailed explanation?

And as asked by the previous poster, is it still the same grammar (sub) point?

Hmm I think I get the nuance, thank you

The way it works with nouns seems easy, but would it works with adjectives too?