I like the bike you've built, and I agree about the $700 pricepoint being limiting for new, and @OP, it would be a hardtail.New? Probably not. ...
you're right. I agree that a $600 2008 Stumpjumper FS would be a great entry point. Also agree used is only viable if ready to take on the bike shop mechanic role. on the pictured bike the headset, fork, bottom bracket, and vbrakes are the only parts not replaced. Fork and front brake disc conversion are waiting for me to have some weekend time (I've built four used bikes this summer, now we're out riding every weekend), I chose to keep the bottom bracket as it was slightly less $ than buying a new crank/bb set for $50. Tool and fluids investment so far around $100 (tubeless is expensive to ramp into, fork oil etc).I like the bike you've built, and I agree about the $700 pricepoint being limiting for new, and @OP, it would be a hardtail.
That said, used isn't for everyone, especially if we look at your example. To begin, you've shown some skill around building, and mention a fork rebuild. I agree the fork is a likely candidate for service, and in most cases that would be a shop expense. Also with used, tires and drivetrain wear components would be a common added expense. Maybe even grips and saddle, depending on condition.
I think the sweet spot is probably a newer used bike - or at least it used to be. The prices there are brutal these days, but you could get some modern features at a reduced price. Top of mind for me is disc brakes - could never go back to rim brakes for cold/wet conditions.
OP seems to be looking for an entry level bike that can do some offroad beyond fire-roads.$700 is only going to get you a HT... if FS its going to be OLD... and something like what Grinchy8 did.
My advice, keep saving.