It's amazing how often this same sentiment is expressed by new Montero owners - I think everybody on this forum has experienced it, that's why we're all still here.

Welcome to the Wire - you've come to the right place to get your questions answered.

Since you're not driving a Jeep, there aren't any bolt-on sway-bar disconnects available for your vehicle. There are kits available that can work but will require fabrication. It's common to remove the rear sway bar entirely, but it will negatively affect your on-road handling. I will remove both of mine before a significant wheeling trip - I can remove or reinstall the front bar in about 5 minutes, but the rear takes more like 45 minutes since the shocks have to be pulled out of the way.

Replacing your rear springs may help with your bottoming issue, but you likely need to replace the shocks also. The KYB Gas-a-Justs are generally considered to be the best reasonably priced shocks, the Old Man Emu (OME) shocks work very well also but are more expensive.

Installing manual hubs is a good upgrade - they will reduce the wear and tear on your front axles and driveshaft (which would otherwise be turning at all times when the vehicle is moving), improve your fuel mileage slightly, and enable you to continue to drive your vehicle if you were to break a CV joint or something in the front end while 4-wheeling. Welding your front diff may not be the best idea if you plan to use your 4 wheel drive for anything other than serious off-roading.

Most questions about your Montero have been asked, discussed, and answered here before, so the search feature is a very useful tool.

Finally, fix your pics - we want to see what you're driving!