The steering is EASY!
As long as you have a pitman arm puller, you should be in good shape. In fact, if you do an SL with help, you'll be more than well enough prepared for the steering.

As for how long you can run 33s without a steering upgrade, it really depends on how worn your current system is and how you drive. Personally, if I weren't wheeling, I might the upgrade a lower priority, but would take things a little easier for the duration.

On... and, I agree, if you're going to do the SL, the BL is a cheap addition. I was with two guys that had done a few before and it was mostly done in a night.