Using multiple suppliers has pros and cons, it gives you the ability to have a large stock profile, so plenty of variety for customers to choose from. One of the down sides is the shipping side.
If a customer purchases products from more than one of your suppliers, then both suppliers are going to have to ship their own orders independently of each other. This of course means that the chances of both or multiple orders arriving at the exact same time are virtually impossible, so your customer isn't just going to be getting multiple deliveries, but it will most likely be spread over multiple days as well.
Probably a smart thing to do is include this type of information on the site to make customers aware of the possibility. It could be very frustrating and confusing to receive on order before another if they're not expecting it. If they aren't anticipating it, they have the potential to make your life hell lol
In regards to shipping, your supplier will be setting the shipping price as they are the ones shipping it. So you need to sort out delivery charges on products with them.