To what extent is the supplication, “O Allah, I seek refuge in You from my idleness, my stagnation, and the delay of my marriage,” sound for facilitating marriage?

There is no harm in supplicating with phrases for facilitating marriage, even if they are not from the transmitted (masnun) supplications, for it is permissible to supplicate with non-transmitted phrases. It is preferable to refer to fatwas numbered: 48194, 67391, 18143, and 61741 to learn about the transmitted supplications and beneficial means.