i have a better idea, if you have enough budget for the lighting.
If you wanna master in lighting for outdoor pictures, i would recommend you to buy one of the Elinchrom Ranger RX Quadra with either a beauty dish or a Softbox, and few triggers.
it will cost you around $800-1000 maybe more.
if you cant afford that, i would say, for this moment, just get yourself a decent triggers, and a Soft-box. i have used umbrellas for outdoors, IMO Soft boxes are way better.
play around with the softbox and off camera flashes . And then if you feel like you need more "power" then go ahead and upgrade.
Good luck