How much bitcoin can I buy a week?

Could you elaborate on the factors that determine how much Bitcoin one can feasibly purchase within a week? Are there any limitations imposed by exchanges or banks? Do market fluctuations and volatility play a role in determining weekly purchase amounts? Furthermore, is there a recommended percentage of one's portfolio that should be allocated to Bitcoin purchases? I'm particularly interested in understanding the practical considerations and best practices for making regular Bitcoin investments. Your insights would be greatly appreciated.