That's a hot potato, zeitun!

The sermon, notices and the reading of the Epistle and Gospel in English are not part of the Mass, so there is no ceremonial attached to them. But the Mass vestments (chasuble and maniple) can only be worn when saying Mass, so the priest should really remove them for the sermon, etc. Because it's complicated to do so, as least at a Low Mass, just the maniple is removed as a token gesture. But it should be removed. I don't know about where the priest should stand for preaching, though.

The congregation shouldn't really stand for the Gospel in English, as it's officially just part of the sermon and was specifically only allowed on that condition, until Bugnini came along. But traditionalists are so used to standing, there's not much to be done. Perhaps it was something that came in under Pius XII to soften people up for having the Gospel read in the vernacular as part of the Mass, without the Latin.

SSPX priests were sometimes doing that in the 1980's in Germany and Belgium, probably copying 1950's practices. I don't know if they still do, but one reason given was that on a Sunday, with the sermon as well, it was too long for the children if the Epistle and Gospel were read in Latin.

(There is at least one SSPX priest who gets out of the standing problem by simply not reading the Gospel in English!)

I cannot find an answer to this on my own:

Is it licit for a priest to keep his maniple on and preach a sermon from the altar?  This is not an accident because it's happened multiple times by more than one priest at the same SSPX chapel.

Thanks.

Some do, some don't. Depending on which rubrics they follow.

Found this.

http://frvanhove.wordpress.com/2011/05/29/arguments-against-removing-the-maniple-for-the-homily-in-the-classic-form-of-mass-extraordinary-form/