I'm about to invest in stocks and plan to invest a small amount (say 500) per month at a maximum total amount of 50,000. Say my target percentages are as follows (they will change in a monthly basis).

Company-A: 15%
Company-B: 15%
Company-C: 35%
Company-D: 5%
Company-E: 30%

Rebalancing is straightforward when you already have a size-able portfolio. You sell stock you have too much of then buy stocks you have too little of.

But if you're just starting, what are the steps to attaining this target balance provided that I only invest a fraction of the maximum at a time?