You'll have to excuse my second post to this as last night I had a bit of Christmas drink and left a few bits of advice out
Clutch: If you know its slipping change it, if its slipping it wont be long before its done. If its not slipping dont bother yet. What I would recomend 100% is throwing that automatic adjusting clutch cable in the garbage and buying a manual adjust cable. Before you install it hang it on a hook or in a vise over night with a good dose of any good silicone spray lube poured thru it. Hanging it lets the extra drip out. Swap over the rubber foot that sits on the transmission and then re use the grommit that seals into the firewall. It litterally takes less time to install it than it took to write this paragraph. Adjust it so you have about 1 - 1.5" of free. play in the clutch pedal. The feel of a nicley lubed cable is 500% than even a brand new auto adjusting cable.
Front Motor mount, you may find you have to remove the oil filter to get the front one out and new one in.
Linkage: The reason you want to get a full set with new bushings and the rods is so that everything is nice and tight. You can still order them with VW part numbers from any good VW parts store because they still make them. While your there try and buy either new or used a weighted shift rod from a Mk3. It makes the shift feel like silk. Before you install all of the linkage bits to the input shaft un bolt the shifter lever itself out of the box and pack it full of grease. Every part of it. This helps tighten up any rattle in the lever itself and also helps it shift way smoother like when it was new.
If you use a factory set of linkage the adjustment is easy. You can buy an alignment tool that sits on the reverse lock out hook and the first/2nd slide on the shift box essentially locking the lever in place, then all you have to do is undo the bolt at the end of the input shaft under the car, watch the linkage spring back to where it wants to be and and then tighten it up. You can use the fat end of a cassette tape for the gap between the reverse finger and side, then the shift knob itself to lock the fore and aft and a bungee cord wrapped to one of the driver seat controls to do the same but I like using the tool. Lube the bushings with a good high heat grease. If you live where its pouring wet all the time like Vancouver I like to take the linkage out and re lube it once a year just so it continues to feel super smooth. If you go with one of the fancier upgraded shift sets youre in for more work. I have a Missing linkz set that is really slick. Moves nice, great manufacturing for a cheap price, heim joints instead of bushings, really tough stuff but was an absolute pain to set up, and even then Im still making small adjustments to it. I found that the upgraded stuff is not forgiving to small mis alignments or adjustment issues. Where as the stock stuff you just have to adjust the position of the shift leaver to get it bang on.If I had to do it again I would just buy a factory set and not worry about a throw reduction.
Just looking at the picture of your engine bay I have some more sudgestions for you.
1-Take the hour out of your life and clean the hell out of the air box and potencimeter. Undoo the intake boot at both ends. Undo the bolts holding the fuel distributer to the air box and then remove the lid. Blast and wipe it untill all the metal bit shine like a mirror. They have a nasty habbit of getting black and dirty since the PCV vents right there. You can use very light drops of a mineral oil or tri flow on the pivots if you like. Do not mess with the spring or the height of the sensor plate at all. If it works leave it. Its just one of those things. Too many people mess with the height and the car never runs the same again. Pour a good sized bottle of injector cleaner into the tank and it will clean out the fuel distributer just fine. Im a fan of Liqui-moly Jectron. Their valve clean also actually works really well. I like to run a bottle of cleaner thru every other oil change since the gas where I am isnt particularly clean but the valve stuff you really only need to do once unless you have some serious pcv mess contaminating the intake.
The other thing I sudgest when you get around to doing an ignition tune up is to stay away from cheap jobber replacement bits. The engine will revolt I can promis you that. In the past I have always recomended using Bosch stuff as thats what the car came with from the factory. In recent years tho Bosch's quality has deminished with most of its production being moved to Brazil. Some of it may still be German made but not all. I started using stuff buy Bremi and Beru. Its German made, stands up to the OE spec very well and works just as good if you mix and match it. As far as plugs and wires go just buy what the car needs. An OE set of wires will last you a few years no issue, and the OE Bosch copper single prong plugs are all it likes. To prove a point once I installed a brand new set of NGK platinum plugs into a car that was getting a tune up. It ran better with the old Bosch copper plugs that had nearly 75000km on them and the gaps were all off. Test the coil!
In the bentley it lists the resistance values for every Bosch coil ever used. Its very detailed aswell - impossible to mix it up. Usually with age the primary goes out of spec. If its even slightly out of spec just replace it as it will only give you a better combustion witch helps everything. Just keep in mind when you test it put your multimeter on the posts themselves, not the tangs nutted to them. The coil is often the most overlooked bit under the hood, usually its only changed when it gets really bad or you have a no spark / no start. My opioion, if it looks old and you really want make that engine sing change the coil.
One cheap way to get a good chunk of power is to ditch the AC. It was the first thing I got rid of in my car in favor of 4 windows and a sun roof. Its rediculous how much HP is sapped by the AC aswell as a deminished fuel milage. On a really hot summer, or if your a wimp to the heat you can have worse fuel milage in the summer than winter. You'll end up changing the belts for non AC equiped engine belts, and then removing the system from under the hood, and the H-Vac. Its a bit of work yes, but It yeilds a noticable improvment. The only other thing youd need to buy is a used face plate from a non AC car, and then remove the electrics from the car aswell. The easy way is to just remove the AC fuse.