If you are looking for efficient cb lvls, speed level early combat stats by doing specific quests, theres acc build guides out there and framed did a video titled like how far can i get a lvl 3 in 24 hrs.
If you want to stay a skiller that'll be tough to make money, I haven't done a skiller personally. You seem to be f2p, but you mentioned herblore so i assume you are p2p as these are mostly p2p methods.
Thieving master farmers with rogues outfit, assuming you can even get that, might be the most gp/hr you could make. R/c'ing mud runes is probably ok money given your options. Selling bh kills, looting, tanning dhides, running bones, and last man standing are ways to get money if you need your first 500k.
Skillers are pretty limited, I dont think you could do bird house runs but black chins would be decent as they're wildy and most ppl wouldn't be able to attack you, but some would still. Farm runs I guess are worth it, not really for gp but you're getting xp at least. Mining and banking iron isn't great but it's xp+gp.
You're gonna need to get a cash stack fast and start flipping imo, I can't imagine how a skiller would get up to zulrah/vorkath/gorillas gp/hr but 1M/hr is doable.