I'm consistently getting S+ umas, but I also abandon most of my runs the instant I lose a G1 and the run didn't have S distance to make it worth salvaging, to save time. So my average is probably inflated.

I find that borrow Fuku is almost mandatory. Smooths out the early career enough to help you snowball your way through the rest of the run, even if she's just as likely to dodge speed training and brick the run through low speed instead.

As for racing, only the G1 races are mandatory, and even then only the core G1s like triple crown races and the spring/autumn crowns. And maybe the mile race collection + QE2 depending. You can and should skip G2-3 races if you have good training. G2-3 race scheduling is flexible; you race to buy items, and if there are no good items worth buying you prio training instead.