From the top!
Cracks in the exhaust manifold are common and usually not an issue unless they are really bad.
Humming while driving is a very strong indicator of a worn wheel bearing, especially if the vehicle has a lot of miles.
There should be slight pressure on the rotor from the pads; this is normal. Having said that I will add that there should not be too much pressure exerted by the caliper, it is one of those things that you have to judge by feel.
You have a bad e-brake cable and there is likely nothing you can do to fix it but to find a good working replacement somewhere. You may have to get creative and adapt something from another vehicle such as a sedan or van or even DSM. CSMs with rear disc brakes are hard to find. Try buying re-built calipers from a parts store. They are normally affordable and well worth the effort. Find and fix the leak ASAP.
Smoking after idling is indicative of bad valve stem seals; smoking while idling and driving is indicative of bad rings. The 4g6X family of engines is known for needing valve stem seals. You will need to replace the valve stem seals. This usually requires pulling the head unless you buy one of these fancy-pants tools:
http://store.kingsperformance.com/produ ... 9-dsm-4g63 Yes it is $90 but I consider the cost to better the massive amount of extra work that goes along with pulling the head off and a new head gasket will run you $60 or so from Mitsu.
Your aged struts probably need replaced. Try some KYB GR2s; I use them and find them to be comfortable but also capable of keeping up with my stiffer-than-stock springs.
You won't be able to just slap a 14b on. The banjo bolts, return hose, water lines and all that mess are different. If you can get all those parts then go for it, but you will probably have to get creative with the bottom water line.
You can't simply upgrade injectors without having the software to compensate for the increase in fuel delivery. If you find a cheap set of injectors then by all means snatch them up. But you will need an AFC or an ECU that has an EPROM in a socket and a friend who can burn you a new tune.
4 lug to 5 lug on the front is easily done using DSM knuckles and CV axles. 4 lug to 5 lug on the back requires a little bit more creativity. A member on here had done that swap using the rear axle out of a FWD DSM. A better method of getting rid of the "captive" rotor design is to utilize the Expo "van" knuckles. They are still 4 lug but my opinion is there is no reason to swap to 5 lug anyway, you can find whatever rims you might want in the 4x114.3mm pattern.
If you decide to swap to a '90 DSM ECU you will be able to run a '90 DSM MAF and the previously mentioned 450cc/min injectors. If you do not have a '90 DSM ECU there is no need to chase after a different MAF. The exception would be if you find a 2g DSM MAF and 550cc/min EVO injectors. Then you could simply swap both the MAF and the injectors and you will be set.
I personally love the 4g61t and you will find that it is believed to be stronger than a stock 4g63 due to the decreased rod length. The weekness of the 4g61 is the piston, specifically the ring lands and the lack of off-the-shelf forged engine internals. My opinion would be to play with the 4g61 till it blows. Then start looking for a 4g63.