IPs- how many? Options

[Mongoose]

Is there a hard maximum to the number of IPs a character can have?
What if they are at this maximum (say from implants / magic) and spend edge for another IP? Or if they take drgugs that grant extra IPs?
Would drugs that grant extra IPs stack with other drugs (such as using both Jazz and Cram) and / or with implants / magic?

And lastly, at what point do you declare spending edge for an extra IP? Any time during the turn? Since movment is tied to the number of IPs in a turn, what effect does this have on movment?

This last question has prompted me to consider a few house rules. First, all turns are treated as having 5 IPs. You can move in all 5, but can only act in as many as you'd normally be able to. And yes, you can get up to 5, but only by using edge. You could get to 4 with implants / magic / drugs, but can only benefit from one drug at a time. Also, you can move twice in an IP by spending a complex action to do nothing but move in that IP (effectively giving up an IP). Yes, this does let charactwers with IP boosting effects move (a bit) faster- at most, you could move twice as fast as normal, if you somehow had actions in all 5 IPs.
Any glaring problems with these house rules?