I’ve been a soloist for many Protestant wedding ceremonies (mostly Presbyterian, Baptist, Methodist, Lutheran, Episcopal, Non-Denominational, Unitarian). The best course of action for you and your fiance is to speak with the music director at the church as to what the norms are for the typical wedding ceremony there.
With the Protestant weddings I’ve done, I’ve found most of the time, the couple will incorporate the soloist for during prelude music and then one solo for any of the “extra” ceremonies you have mentioned in your OP - unity candle, sand ceremony, etc. So, I often will sing between 4 to 6 solos interspersed with the organ or other instrument(s) during the prelude, then usually one solo during the actual ceremony. If the couple really like the voice as an instrument, they will also use the soloist for one or all of the processionals - mothers, bridal party, bride. Sometimes, I have also sung a solo within the ceremony with nothing “going on”. Sometimes, the minister or the music director will recommend a meditational vocal piece after the vows are said and that’s why the extra solo is sometimes used. So everyone will bow their heads in prayer as the music is happening. Other times it is the couple who requests the extra solo as a meditation or something similar.
I don’t know if it would be important to you to have an “Ave Maria” sung during the ceremony, but I’ve done them often at protestant weddings as well. So, it might be permitted by the pastor if you ask. It was a little surprising when I first started singing for non-Catholic ceremonies, especially for the Baptist, Methodist, Presbyterian and non-denominational weddings, how many will request an “Ave Maria” (usually the Schubert or the Bach-Gounod) for their meditation or as their processional… with the “ok” from the ministers. Sometimes, the ministers will suggest it.
Also, as mentioned previously, if you haven’t done so already, make sure you have already received a dispensation to marry outside of the Church.