If you're just playing BS for fun, I recommend flat betting a small amount. If this is the case, then you'd want a bankroll of something like 10 units (very short outing), 20 units (longer outing) or 100 units (multiday).
You can always play with less, but you may bust out sooner than you planned.
If you want to practice counting, my first advice would be to practice A BUNCH in ways that don't cost you any money. Kitchen table, software, etc.
When gambling with real money, especially if not much of a BJ player anyway, consider "acclimating" yourself with very small spreads (2x, 3x).
Thirdly, the rule of thumb is 100 units of your MAX bet (5-50 spread -> $5000 bankroll). I'm unsure if this is assuming a non-replenishable bankroll (professional gambler) or replenishable (you can rebuild with BR with your day job).
Now, personally, I'm out of town and very near some casinos at this moment, and I've been playing a lot. My BR at the start of the trip was $500, 100 times the table min of $5, but only 20 times my big bet of $25. I am running a significant chance of losing my BR, and cutting short my gambling.