If you're comfortable setting up a flash shot digitally (presumably by iterative tweaking of settings), then do that, transfer the settings to the film camera and take the shot again on film. If you also have a flash meter, you can measure what lighting looks good to you and then use those ratios in future.
Similarly, you can setup a shot as if you were shooting film, but take it on digital with the rear LCD disabled. Do a whole bunch of them, and then don't review until the end of the session. You'll learn whether you're making good lighting decisions without spending any more money.
As for colour portraits, Portra is where it's at. You can+should do your own B&W development at home, and there are plenty of excellent and affordable B&W films to practise your portraiture with for less money than the colour costs. Some of them (TMX, Acros, Pan-F) are also finer than just about any colour offering so you can make excellent prints up to about 12x18 without them looking too much like 35mm. If you're really cheap, you can bulk-load 35mm film from 100-foot rolls.