Micro Wedding

Congrats on the wedding! Micro weddings are my absolute favorite! They are so intimate and romantic 💕
As far as seating, I would just have everybody seat themselves. The purpose of ushers is to ensure everyone is seated efficiently when dealing with a large crowd. But since there are only 18 people, I’m sure everybody can efficiently seat themselves.
TBH, I haven’t seen the unity candle or sand ceremony done in over 10 years. However, if that’s something you really want to have done at your ceremony, then you should do that! If it’s not something you want, feel free to eliminate it.

I don’t think an usher will be necessary with only 18 people, unless you have super specific seating plans. If you want to do a unity candle or sand ceremony, then do it. The size of the wedding doesn’t matter on that.