New paph owner! Yellow leaf. Does it look ok?

[Paphluvr]

As rbarata says, it's just a sign of normal aging. As long as it's the lowest leaf turning pale, then yellowing and eventually turning brown and drying up it's normal. As far as your watering schedule goes, twice a week in sphagnum might be too much. Does the pot feel significantly lighter when you're ready to water again or is it still heavy? Also, Paphs can be repotted at any time. Most growers will repot a plant soon after acclimation in order to get it into a mix they're familiar with and to assess the condition of the roots.

Your light exposure sounds good. Night time temperature
sounds OK, but your daytime temp is a bit chilly. Usually 10-15 deg between night and day is better, all the more reason to get it out of the sphag.

In your first photo I see the stem but no bud. Did you buy it in bud or did the spike develope in your care? It looks like the bud has been broken off (sad to say).