There's not much you can do about precision fitting without spending dough to replace things such as handlebar stems.

On the bright side, there's not much needed for your purposes, unless you have unusual proportions, so odds are you can do a DIY fitting that will be at least 95% as good as what folks charge big bucks for.

There are a number of sites offering fit guides, but the best guide is your own body.

Saddle height is such that your heel just reaches pedals with your leg straight (hips not rocked to reach). This gives you a slight bend at the knee when you move your foot back so the pall is over the pedal spindle. If you use toe clips you want the length so that the ball is over the spindle.

Saddle should start out centered over the post so the post extended would go straight up your ......

Saddle tilt, start roughly level, and adjust the nose up or down a few degrees to counter any tendency to slide forward or back.

Handlebar height for most new riders is usually at the maximum, though it shouldn't be higher than the saddle unless you absolutely need it that high for comfort. Most experienced riders end us lowering bars after awhile.

Now a fitter, would first locate the saddle forward and back based on pedaling, but you don't want to buy a new stem, so ride a while, and if you feel your either reaching for the bars, or feel they're too c,lose, adjust the saddle forward o back to correct. If you cannot get comfortable, then you'll want help selecting a new stem, which will give you the right height and forward extension of the bars, but the vast bulk of riders do OK with what they have unless the bike comes with a disproportionately long or short stem.

Those are the basics, ride that way a while and settle in so you know what you don't like, and might want to correct, but no fitter can properly fit a novice rider, because the riding style isn't developed yet, so there's no sense spending dough until you know why.

BTW- I didn't mention fitting the frame because you already have it coming, so that bridge has been crossed. However if you can't stand over the top tube with room to spare, it's too big for you. Likewise, if your raising the saddle to the max height, odds are it's too short.

Lastly, the best place to get low cost help with a mail order bike is a local bike co-op, since they won't resent the lost sale. If you add your city of residence to your profile, someone might know if there's a good one near you, likewise with a reliable fitter if it ever comes to that. There are also lists of bike co-ops by state on the internet.