I just started playing Rising Star three weeks ago. I began without investing anything as I don't have much money to spare at the moment and also set some goals for my Hive and HBD wallet :) .
I just read the FAQ but did not get that you could actually stack the cards. I found the "Band" page misleading as you can choose one card for the vehicle
My goal at the moment was to buy an energy boost as I learnt some days ago that they were "recharging" (thanks 
I can't tell why, but I decided to buy a second "T2 mid range tour Bus" as they are dirt cheap (1740 starbits) at the moment. And I was delighted to discover that they actually stacked ! (and can't buy enough to access the Saturday Support)
So, I just bought enough Mid Range Tour Bus to have a continuous access to the Midweek Headline Slot which has a much better Starbits to Stamina ratio than the previous missions.
I'll have to go through some Singing lessons to reduce my Ego, but I'll most probably get much faster back to the point where I can buy my first energy booster !
The game just got much more addictive for me !!
By the way, if you know some good beginner posts about Rising Star, I'd be happy to read them!