Thanks for your question.

Here are my thoughts:

1). As you mentioned, VEGO beds have no bottoms. They are designed to sit directly on the soil. When you mention using landscape fabric, I assume you are thinking of placing the fabric on top of the soil and then the raised bed on top of the fabric. This is not normally recommended. This fabric would impede good drainage. Also, it would prevent earthworms and other important soil organisms from moving upwards into the raised bed itself.

2). Instead of fabric, put down two or three layers of cardboard on top of the soil. The raised bed then goes on top of the cardboard. This will enhance the soil under the raised bed. After a year or two, the cardboard will have broken down. In the interim, this cardboard will not significantly affect water drainage. Once it has decomposed, earthworms and other critters will be able to move upwards.  It will also serve as a deterrent for weeds growing up into the raised be

3). For a raised bed this deep, you are spot on in thinking that it need not be filled completely with dirt. For a bottom layer (between 8 and 10 inches) that will be sitting directly on top of the cardboard, put down sticks, branches, and/or wood chips.

4). On top of this bottom layer, create a middle layer (10 inches or so) of composted material, leaves, straw, and/or mulched lawn clippings.

5). Now create a top layer that will be 7 to 10 inches in depth. This will be the home of your strawberries. OMRI is a good product to use but it should be a component of this layer; not the only thing in it. As it comes from the bag, OMRI compost is quite light, even “fluffy”. At the minimum, have a top layer of 50% OMRI and 50% topsoil (NOT potting soil).  Thoroughly mix the two together.

6). When raised beds are first established and used, there is reduced water retention. This could imperil your newly transplanted strawberries. In the raised beds that I have constructed, I have found that I had to do considerable watering after planting. The soil seemed to dry out quickly. To address this problem, for a top layer I now use about 40% compost, 40% topsoil, and 20% coco coir or peat moss. This latter component significantly increases water retention, which is what you will want for your strawberries.  I mix all three together.

I have attached to my answer an image showing these layers. Also see the following for further information on these and related points:

https://www.vegogarden.com/blogs/academy/why-you-should-put-cardboard-in-your-raised-beds-1

https://strawberryplants.org/growing-strawberries-in-raised-garden-beds/

Good luck. Please feel free to get back to us with any other related questions.