You are running a high risk
Your risk of ruin is quite high, depending on the penetration you are getting in this game. It would run from about 34% at 50% penetration, which is quite common on single deck games to just about Kelly levels if you could get 75% penetration, which is quite rare.
A 1-5 spread could be used at this betting level without too much heat in most places, but there are exceptions to the rule. A good betting spread for 1-5 in single deck would be;
1 unit at counts of less than +1, 2 units at +1, 4 units at +2 and +3 and 5 units at +4 or higher.
Unfortunately, with a $900 bank, you have a high chance of going broke. But, you do have a better than even chance of doubling that bank and if you lose the whole shooting match, you haven't lost much, all things considered. If you do double the bank, don't raise your betting levels quite yet. If you can build to a $3K bank, you might consider raising your bet levels to $10, but not before that.