Fees to create a limit order or change a limit order should be the lowest possible, imo. In all normal trading platforms, there is no fee for modifying your order, so charging a fee of any significance drives traders and market makers away from the service. If it wasnt for the need to prevent spamming, I would say there should be no fee, but we can't have people eating up our 100k TPS with bot trading modification spam.
I think even 1 cent might be too much and we should strive for .1 cent. Otherwise you are going to make people not want to run market maker bots.
Fees for executed trades can of course be higher.
Fees to publish feeds should also be extremely low, since we want feeds to be published often.
I like that the market order fee is a percentage. Many trading platforms have, for example, a 0.2% fee. (Btc38, etc). 0.2% is a reasonable value for this, imo. (And premium or lifetime account subscribers would get a discount to it). Alternately we could try 0.1% to undercut competition.