I'd recommend merching on the side while doing something productive. You double your profits that way. If you're going to merch, you need money to buy items in bulk, otherwise you wont be making much money.
Join the clan chat FFDN36. You can run double nats with your own pure ess (they dont trade back noted ess) which can prove very profitable if you use the abyss.
You could always make money quickly on RS3 and then use a gold swapping service to change over to 07 gp. The best money making methods on RS3 are about 5m per hour I think, so you can get about 1m 07gp in 2 hours. Which is quite decent.