As has been pointed out by others, there already exist databases that annotate many key metabolic pathways; however, I think the reason the database you describ

As has been pointed out by others, there already exist databases that annotate many key metabolic pathways; however, I think the reason the database you describe doesn't exist is that there's a LOT more very customized work in recreating synthetic pathways in cells. Minimally, as you say, you'll produce plasmids that code for all the proteins you need. In practice, factors affecting your design decisions include, but are not limited to: * What your ultimate goals are (proof of concept versus lab/industrial-scale synthesis) * Your synthetic vehicle, i.e. in which organism you will be recreating this pathway * Whether the relevant pathway/genes already exist in some form in your vehicle, and may be affected by an introduction of foreign genes * How you will detect expression of your foreign proteins (the fact that your genes are expressed doesn't mean the corresponding proteins are produced, and if you can't confirm protein expression, the inevitable troubleshooting will be five kinds of hell) * What kinds of promoters you'll need to drive gene expression * How stable the proteins in this pathway are, and if you need to modify them to increase stability * Whether your proteins, after being produced, need extra tweaks (post-translational modifications, in the parlance) in order to work * How much DNA you'll need * How you'll deliver the DNA, i.e. what size/kind of delivery vector * How you'll make the delivery vector * Whether your proteins will fold properly once produced in the vehicle, and whether they will localize to the right parts of the cell * Whether your proteins are toxic to your vehicle cell *etc.