bottom feed is great for soil, but less than optimal for soilless... can make it work with an occassional top-down irrigation but the point of automating is to not have to do things by hand. One of the primary benefits of soilless growing is easily maintaining a consistent level of nutrients in the medium through the 10% or more runoff. Bottom irrigation removes that benefit.
diy it.. avoid adjustable emitters and manifolds. It sounds like a good idea but only results in 10x more work getting things dialed in and then any small change to one requires adjustments to all. pressure compensating emitters are you best option and easy to use.
e,g, when i start shutting off pots at harvest, i don't have to runn around like a chicken with its head cut off adjusting every manifold and every adjustable emitter. then repeating that process 2-3 times to balance it out, because again, changing one impacts all others.. if i get an emitter with a slight clog (even if not relevant to getting the job done), i don't have to adjust every manifold and emitter etc etc... "ajdustable" is the devil.
simple pump with float switch can handle runoff. As far as irrigation pump, don't buy aquarium pumps. buy the type they use to boost RV shower pressure and such. You need the 45-60 psi not high flow rates.
really only worth it if you have a larger garden. 1-2 plants is just a few minutes to water and easy to take any waste water away, but it quickly becomes a time-sink if you expand.