No grinding or welding is required for the 4:1 gearsets. The current gearsets are billet, and simply replace the original gears. There are some how-to's online if you choose to do it yourself (I paid Trailtough to convert mine). This might be a good opportunity to rebuild/overhaul the T-case, while you have it apart, even though it may not yet need it.
Stock drivetrain should be fine for the 4:1 T-case. It is, in the end, a matter of terrain and driving style. If you stay with small tires, say 30" and under, you are less likely to increase stresses to the breaking point.
Ultra-low T-case gearsets are 6:1 and 8:1 and are often used with much-larger-than-stock tires. This combination almost mandates something like TT's MightyKong, one of the most popular cradles. I run a 4:1, stock T-case arms, a Detroit locker and 28" tires -- no problems for me so far. But I will reinforce the stock T-case mounting arms someday soon, just because I can. I'm sure others will have opinions as well.