I want to combine 3 iRules that are all redirects without "too many redirects" error

Here is an example of how I would run through this issue:

when CLIENT_ACCEPTED {
switch [TCP::local_port] {
"443" {
set proto "https"
}
default {
set proto "http"
}
}
}
when HTTP_REQUEST {
switch -glob [HTTP::uri] {
"/investors*" {
if { ($proto equals "https") } {
HTTP::redirect "http://[HTTP::host][HTTP::uri]"
}
}
default {
if { ($proto equals "http") } {
HTTP::redirect "https://[HTTP::host][HTTP::uri]"
} elseif { ([HTTP::host] equals "domain.com") } {
HTTP::redirect "$proto://www.domain.com[HTTP::uri]"
}
}
}
}

The basic concept is - you can have multiple HTTP::redirect commands in a single iRule, but no two can be logically reachable at the same time. So long as the logic only allows one to execute in any given request, you should be clear. Switch and elseif's eliminate the potential for multiple executions.