Although you could do it via long distance, since you will be in the DR for 20 days in December, I would really encourage you to go to the factory. Before you go, look through magazines showing rattan furniture and think about what you would like. If you should see something that you really like, they will duplicate it for you. Also, by doing your homework, it will give you ideas as to how you might modify the furniture they make.
When at the factory, don't just look at the "samples" in the display area, walk through the warehouse. Some of the furniture we ended up buying we found in the warehouse. Also, if you see something you are interested in, but would like it a little different, tell them and they will make yours to your specifications. We did that with several pieces that we bought.
With respect to the fabric, at the time we bought our furniture (about 1 1/2 years ago) the selection wasn't large. But there are a couple of fabric stores in Santiago that have a great selection, including imported fabrics. So we asked the factory for the quantity of material required and bought it at the fabric store. The factory gave us a credit since we hadn't used their fabric. It was the difference between choosing what we liked best from the selection of the factory, or getting exactly what we wanted. Since this will probably be our last home, we wanted it furnished the way we really wanted it to be.
Everything that we did leading up to the ordering of our furniture could easily be done within the period of time you will be visiting. When you place your order, you will need to make a substantial down payment, then pay the rest when your furniture is delivered. Tell them what your schedule is and they will program the preparation of your furniture accordingly.
During the interim, you can communicate with Yolanda (who speaks English) by email. Should you have a brainstorm about something you would like done or changed, you can communicate this to her by email. Up to the time they actually start on your furniture, you can make changes.