It is not that hard to properly expose slides, but it is important to be observant and aware of the light. Go for a day with even light, especially to start. A cloudless day is best. Nothing is more frustrating than watching a scene change two stops in less than a second. Also, a clear, blue sky meters about the same as the ground that it illuminates.
Lose the spot meter and and forget about "...trying to keep the highlights within 2-3 stops or so...". If your camera has a center weighted meter, preferably Thru the Lens, use it. Otherwise, use a standard reflective meter. With a handheld meter, bias it toward the ground; it is easy to pick up too much sky. Once you have take hundreds of properly exposed slides you can break out the spot meter again and start working with more complexly lit scenes.
Pick an average scene, evenly lit, with the sun somewhere around 45 degrees or so behind you. Look for overly dark areas or specular reflections that will effect the metering and the final image. Shoot between mid/late morning to mid/late afternoon, depending on the time of year. Forget about that "magic, crepuscular light" for now; it is very challenging to get a good shot under those conditions.
Just don't overthink it. I shot two rolls today with seventy year old cameras. The meter was a sixty year old selenium cell Ikophot, which I only checked a couple of times. The sun was high, there was a bit of haze, it was an f11 day and that's where the aperture stayed. The pictures all came out beautiful.