Re: Need some help with design
Not sure about dowels for this application.
I would use chunky splines. Yellow glue if you get nice fit, epoxy if the hand is not that steady.
If you don't have sufficiently long clamps then indeed, screws could be use as clamping devices. You have a bunch of elements that appear to have more than sufficient combined gluing/fastening surface. Auxiliary screws (in addition to glue) from underneath will do wonders too. Through bolts might be an overkill but surely an effective one. The bottom shelf seems to be placed between the table's legs. Glue it and screw it to the legs from underneath. The legs wont let the frame go apart, and the frame elements won't allow cross members to move away from the legs.
Unless I completely misunderstand the drawing, this structure will be rock solid as a result of combination of glue, fasteners and positioning of elements in relation to other elements.
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