I like the design feature, that permits adjustment of the stop collar.
It will allow you to fine tune the drilling depth.
Make all your design plans and drawings before proceeding.
Where applicable, make full size patterns, before cutting the wood.
Patterns can be made from poster board material---
use packaging tape across the pattern joints, for larger size pieces.
I'd make the top planks from 2x8's, edges butted, and use an overlay panel of 1/4" tempered hardboard, over the 2x8's. The overlay can be affixed using construction adhesive. When it get damaged, it can be replaced.
Extend the ends of the 2x8's, far enough beyond the legs, to allow bolting of a vise on either end of the bench. (Mine is about 10").
Plan for bench dog holes in your top.---very handy to have for working wood---planing, sanding, assembly, and the like.
You can also plan for a wood workers vise, to be located on one end.
They will come in very hand for many tasks. ( I have one on one end, and one in the center.
Diamond plate looks nice, but---not practical for a work bench top.
A smooth surface is the way to go.
A metal work top surface is more suitable, for doing metal work.
Use 1/8" hardboard to make patterns. 1/4" is better if you plan to used a router and trim bits.
For the hydrant, you can use a gal size plastic contain, like a mini 5 gal water bottle, or gallon size an ice tea jug (it contains a spigot). Cover the outside with wood slats or strips, akin to barrel slats. Fill all the joints with silicone caulk, so as to make it smooth, and paint it. The slats can be bonded to the plastic with silicone adhesive.
I think it would look pretty cool.
Make the emblems, with the details carved into 1/4" thick wood.
(Carving can be accomplished using inexpensive carving tools, available from craft stores. Give the carving chisel edges a keen sharpened cutting edge).
Finish with the desired accenting, details and colors.
Mortise an area into the bench, to accept the desired item(s)---
akin to making an inlay.
The emblem could be made flush with the surrounding surface.
(Mortise out an area, to accept the inlay emblem. A mortise can be chiseled out, or use a router and square up the corners).
If making the legs from 4x4 stock, the emblems can be fitted into the legs.
Most of the prep work and making of the smaller items can be done before commencing with the build.
(One can accomplish many of these tasks, wearing a cast or confined to a wheel chair).