In general for tenmokujawan, L hand does NOT HAVE TO HAVE PINKY TUCKED WHEN WHISKING!!! Just have L there and on the seam steadily, does not need to be tucked
During nakadachi, yes you do shikko to mizusashi to put into midare, then shittai back to knee line, then shittai again to exit. However, new revelation as of today, you never need to go beyond the knee line (even for mizutsugi). You just need to get up to the knee line, but be centered on mizusashi shomen. So during nakadashi, you don’t necessarily need to shikko - you could just slide to the right. Same for very end when refilling mizutsugi — you sit low, but shikko up to THE KNEE LINE.
Mizutsugi, make sure to place it centered at temae (ie daisu shomen, but also centered vertically in the space). Same goes for usual hirademae as well.
Also, if using tana, try to have the spout outside the bounds of the tana (so you make sure you have enough room to open the mizusashi lid)
Also, for daisu, remember that the kensui is not necessarily centered. Center of daisu may be more to the left (for furo).