So I've been looking for a mod that add equipment grids to trains for my seablock playthrough, and encountered your mod here.
I like the approach of using an equipment grid train car, instead of the locomotive, probably saves you a lot of headache with compatibility with various engine mods). Giving your wagon access to adjoining cars is innovative interesting.

This makes it a Good mod IMO.

... But... I have some feedback that could elevate it to a GREAT mod, (from my point of view anyway). My primary nitpicks are around balance.

Comparing costs with vanilla, I appreciate that you've added complexity (red circuit) to add a feature (equipment grid, and storage push/pull), and the added weight will have an effect on train acceleration/top speed/deceleration and thus fuel consumption.
I think the costs are about right for adding an equipment grid similar to that of a modular armor (also built using red circuit) 5x5, maybe buff it to 5x6. Not the 12x12 which is more than what a Mk2 power armor can support and it uses blue circuit).

You've more than doubled the cargo capacity from a default wagon; a wagon that has the ability to push/pull from adjoining cars.
As it stands there's little incentive for me to use any wagons other than this one because it is categorically better in every way (except weight), and even most other mods wagons.
I'd like to suggest going the other way and given it 10-20 cargo instead of the default (40). Explained as "The components for the equipment grid and getting resources from other cars takes up part of the cargo wagon's local storage" and then maybe keep standard 1000 weight or possibly double.

This also paves the way for a mk2 and 3 models, recovering some of that lost storage, and bumping up the equipment grid to 'power armor mk1&2' levels (7x7 & 10/10 respectively), which would still be more than a Spidertron's grid... I'd keep cargo to no more than 40 for this line of wagons with access to the push/pull mechanic. And improvements in technology could also help reduce that weight.

I'm incentivized to use other wagons for storage volume, and the construction wagon for my construction jobs... if I just really want to throw more robots at a task, I can use more constructions wagons, at the cost less cargo, or more locomotives to pull the extra weight.

I don't know if you have an interest in further designing this mod or not, or maybe you have your own ideas on where to go from here.

Anyway, this has just been my unsolicited attempt at constructive feedback.

PS. I'd like to see an adjustment of the science cost/requirements to bring this in-line with bob/angels/seablock progression.

Sorry been mega busy with programming projects :(

I think the costs are about right for adding an equipment grid similar to that of a modular armor (also built using red circuit) 5x5, maybe buff it to 5x6. Not the 12x12 which is more than what a Mk2 power armor can support and it uses blue circuit).
You've more than doubled the cargo capacity from a default wagon; a wagon that has the ability to push/pull from adjoining cars.
As it stands there's little incentive for me to use any wagons other than this one because it is categorically better in every way (except weight), and even most other mods wagons.

if I just really want to throw more robots at a task, I can use more constructions wagons, at the cost less cargo, or more locomotives to pull the extra weight.

So main problem I had here really was Factorio doesn't allow the vehicle equipment grids to directly access other wagons. Which is pretty much why I made the whole auto-transfer thing to start with so would only need 1 slot of items and only need a few for destruction. If you try having 5 wagons each with their own small grid I had issues before because the robots don't really "cooperate" and the areas don't fully overlap.

Vanilla already has a lot of buildable items, and with some mods adding new belts, inserters, assembly machines, etc. can be a lot of things would be nice to build :(

The extra weight was basically to try and make it suitably heavy so would prefer other wagons.
An idea I had previously was to try and force extra wagons (so isn't "free space" and is far worse for network congestion), but I don't think can stop people using those slots, since the auxiliary wagons couldn't stop someone using the inventory or grid space practically :( Well could maybe start dumping items on the ground if they are missing or something?

modular armor (also built using red circuit) 5x5, maybe buff it to 5x6. Not the 12x12 which is more than what a Mk2 power armor can support and it uses blue circuit).

Well probably the solution is to (have an option since I know some other mods specifically add them to most wagons/locomotives) to prevent shields, laser turrets, etc. being added. I think being able to have an entire train have far more range, robots, and power than a personal armour makes sense. Could maybe also make a different roboport item.

Main issue is then playing nice with other mods since a lot do stuff with the equipment grid definitions.

Range especially since the track is less flexible.

EDIT: I guess the other issue is for multiple tiers of wagons, roboports, etc. It would be really nice to have some better unique icons :) But somewhat a separate issue