You could easily compartmentalize each investment objective in a spreadsheet while commingling all positions in a single account. That avoids 4-5 EOY tax forms.
With 4-5 accounts, dividends received would be spread out across them and it would be harder to accrue enough cash to buy round lots, unless your broker offers dividend reinvestment for every position.
I would suggest having funds at two different brokers in the event that one is inaccessible so that you can trade at the other should you need to defend your positions. This would apply to a trader rather than a buy & hold investor.
And as Ben mentioned, with multiple accounts, your broker(s) will not be tracking wash sales and could not only lead to a nasty tax surprise but doing it yourself and doing it correctly can be a royal PITA if you have multiple buys and sells after incurring a violation.
I don't see any great advantage to having 4-5 brokerage accounts.