It's possible to run more, but you shouldn't.
Less short Answer?
I'm getting ready to launch what is my 3rd personally created crowdfunding campaign (4th if you count crowdlending), but my 12th crowdfunding campaign all together. I'm starting on IndieGoGo and simply going to put up a landing page for a platform that I'm not actually going to run in tandem on. That is until/unless the link gets clicked often enough. Or if my campaign is taking off and going past its goal fast on IndieGoGo, maybe. Then, with my plan and my assets teed up already, I can quickly spin up a second campaign on that platform as well. It's not building the campaign thats hard, it's driving the traffic that is crucial and really really hard. I'd only do it if we are soaring and I know that we'll get featured by the second platform. Even more realistically though, I'm going to have my own site ready to take pre-orders so that people who find my campaign on IndieGoGo and don't back it, but do Google search for it, won't be left out. There is a right strategic time to be on two or more platforms at once, but the odds that you or I are lined up for it are microscopic.
If stepping up to the plate against a MLB pitcher, are you going to bring two bats to the plate or one?
I'm picking IndieGoGo because I have a community that leans that way and a successful campaign that closed on there. It's also a better fit for my product, if it were a more Kickstartery product, I might go that way instead.
Really long answer?
It's simply this, people who discover your product on a platform and want your product enough to buy in are very rare. Why does the Death Star work? Because it focuses all of the power of a Sun into a point and aims it at one target. You have to be a Death Star to kill it. Most likely you're going to have to go in and take the planet by fist, so don't get too excited there young Darth.
A runaway success on one platform is likely to run away on the second platform. True! Though I've never seen someone not back a campaign because they saw it on a second platform. If they are going to back you and share, they'll probably do it before they ever know about the second platform. If they really love you, they are going to back you again and share (I'm talking about your mom) and their friends are not going to notice the duality. They will subconsciously see the message more times and be slightly more likely to click.
There is an idea; being that if your product is catching all the right eyeballs, there are many people who are already on one platform (or clicking facebook/twitter/linkedin links) who won't join a second platform just for a quick reward. Especially if they are seasoned funders because we really fund you before our intelligent mind catches us. That we do to support you though since we have learned that we will never get the reward that triggered us in the first place. If we do, it will probably suck. The reality is, nobody will see you on one and think, "hmmm, I don't want to join this platform, why don't I go check another one to see if I can buy with one click?" If your product is that good, those four backers aren't going to break you.
Rocketbook is the best two platform product I can think to use as an example. Ask yourself this though. How does a person get to your page and why do they back your idea/product? Someone I knew backed Rocketbook, the name itself caught my attention, I clicked through from my email that Kickstarter sent me saying Luke backed this thing. In 2 minutes I just knew I had to try this and $20 was no big deal. I backed it and got my Rocketbook. It's useless because I have to keep a special pen with it and I don't want my erased notes to come back to haunt me with a freezer. I still love that campaign though. Okay I kinda like the product too, but don't buy it and hate it then say I told you to buy it.
The logic being that you're spending $20K to create and market something, hoping that you can raise at least what you spent, but really hoping that you strike gold and soar into the stratosphere. Feeling sore might be more likely than soaring. Most campaigns have to claw their way to their goal just to make sure it wasn't a wasted investment in the first place. Then you're exhausted and finally admit that you set your goal low so you wouldn't take a total loss on the cost of creating the campaign. Now you you have to deliver and hope that the success comes later on. Not the case on two of the campaigns I worked on, but definitely the case on all the rest. So with that being the probability, focus on one platform up front. If you soar, a week long delay to reframe the same video and pitch to land it on a second platform isn't a deal breaker. In fact, you can edit your first campaign right before it closes, and yes, even get away with saying "our campaign here has come to an end, but there is still a week left over at XYZ platform, hurry don't miss out." You can also email that to all of your backers. Something about a campaign closing funded makes us feel all that more sure that the rewards will actually ship. We might actually finally tell a friend to jump in with us on the second platform since the first door is closed.
If you're looking at flagship campaigns that have raised millions on Kickstarter or IndieGoGo or in tandem. You're missing the point. These products are usually built with pre-funding. I know one IndieGoGo campaign that had $2M in VC capital in their hands before they even strategized their campaign. Did they raise a lot of money? Yes, if you consider $350K or 520% of their goal to be successful when they already had $2M in hand. I saw another one that ran on both platforms. Again $6M in seed before they made their video. If I recall right, they didn't raise $2M on both platforms combined, but they ended up in the Apple store. Success isn't usually as magical as it seems. If you're rolling up your sleeves with those kinds of dollars, you can pull it off. The entire thing is a marketing plan not a fundraising plan.
Could you get lucky with a product that goes viral? Yes. In that case you don't even need to pay the platform and merchant services 8%. A video on YouTube would be enough to get you accepted into an Incubator. Of course YC is going to take 6% of your entire company not just your first cash. Glowforge, while also well funded before hand, blew away Kickstarter numbers with their own campaign on their own page. They can also get away with things like stating that they sold the full retail value of their products, while only collecting the sale price of 50% of the actual MSRP. Since they don't have to follow a platform's rules. And again, they don't have to pay the vig to a platform. If I were them, I'd have run an IndieGoGo and Kickstarter campaign too, but with limited rewards. It would have been worth it for the additional marketing boost. And technically it's not too late except that there is a lot of chatter on the internet about missed deadlines and refunds.
Plan everything out in steps and when a step is huge, put steps underneath it. Crowdfunding is a big steak, take small bites and eat it all. You'll enjoy it a lot more than if you try to fit it all in your mouth at once. Don't plan on doing anything else while you're crowdfunding either. It's a full time commitment.