Sorry for the tardy response, Tom. This is the busy season for art in Hawaii, and I've been swamped.
For the service station, I had mine replaced by HP while I was under warranty, but don't think that a full replacement is absolutely necessary if the wipers are in good shape. HP's solution to all repairs is to just swap out complete assemblies, and I'm sure that is the simplest thing, but I bet that part is pretty expensive if you have to buy it a la carte. If it is mechanically sound, the critical part is the rubber wipers that clean the bottom of the printheads. Those seem to hold up pretty well. I haven't tried cleaning the ink tank in the service station, and would bet that it is rather messy to do, but see no reason why it couldn't be cleaned out in the interest of saving money. You will probably find lots of ink, but take consolation that it is probably a fraction of what you would have to deal with if you owned an Epson wide format printer.
For the spittoon, that is an easy fix. It's just an absorbent pad, and you can wash it out and revive it pretty easily. I suggest that you clean it in a sink and then smash it between two flat plates of something with a vise or c-clamp to really wring it out, so it doesn't mildew.
I think that the belt tensioner is a pretty robust part, and am still on my first one. Unless you have some sort of warning sign, I wouldn't expect you would need to replace it.
The cutter assembly is probably pretty cheap, so you might want to swap that out. I replaced mine from my low mileage parts printer, just for good measure, but I never really had any issues with the original one. It is easily replaced without opening the printer up (just remove the left end panel), so you might want to pull it out and lubricate the track and cutter and see how it performs afterward before buying a new one.
For the aerosol fan, I have replaced mine once, and cleaned it a couple of times. You will probably be astounded how much ink collects on it, and I think that the added weight of the ink on the blades eventually wears out the motor. It's also a pretty easy thing to replace without a complete teardown like the belt, and I'd probably just pull it out and clean it for now. It looks to be a really run of the mill muffin fan, so you could probably find a replacement at almost any electronics supplier.
Other things: I'd pull, clean and lubricate the plastic bushings in the carriage. There are two c-shaped ones that run on the rail, and a little lubricated plastic glide on the back side. It's astounding that they work with as many duty cycles as they do, and I would have expected a much more sophisticated linear bearing would be needed, but I guess the proof is in the pudding for them.
There is an oiler in the upper right side of the track that also lubricates the top carriage track/bearing. It is a weird wick type fabric, and it seems to get chalky and brittle over time. You would probably be well served to look up a part number for that and get another one.
ESP stands for Embedded Photospectrometer. That's your color sensor.
For parts, I would read over the pertinent sections of the service manual and get the part numbers there. I haven't found any source that carries a complete selection. Most have somewhat limited selections, so you sometimes have to get them piecemeal. There are several places run by ex-HP techs on eBay. Use Google shopping, or other web searches to make sure you aren't getting ripped off. When I thought I needed a Media Advance Calibration Tool, I found prices for that glorified screwdriver that ranged from $45 to $1,700, so you really need to do your homework.
