It isn't better to get "bath salts" - it is better to get the pure product and weigh out a smaller dose. For one thing you don't know what the "bath salts" have been cut with, and for another you don't know how cut it is, so you have no idea what the dose you are actually consuming is. Selling chemicals as "bath salts" is dangerous and unethical imo, and I wouldn't want to encourage vendors to carry on by giving them my custom!
MDPV is very, very fiendish so I'm glad you have taken precautions against taking too much. As stimulants go it is relatively physically benign, but has a high risk of fucking with your head and causing stimulant psychosis especially after a multi-day sesh with no sleep..
For the come-down I recommend the same as for any stimulant comedown - sleep, food (or milkshake/protein shake if you can't eat), vitamins, plenty of liquid to rehydrate yourself, having a shower/bath, making yourself comfy, distracting yourself with tv/film/book/computer game, sex, and lots more sleep.
The initial rush is short lived for me, much like cocaine, but the residual stimulation without the actual high can linger for hours after your last dose, so watch for that. Benzos help. Be careful you don't drink too much beer and dehydrate yourself (and as always go steady mixing benzos and alcohol..)