My husband and I just brought a 2002 Mazda MPV

My husband and I just brought a 2002 Mazda MPV. While driving it home the van began to buck like it was having problems shifting, the battery light also came on. Then when we parked the van we notice a white smoke coming from under the front passenger tire. We open up the hood but did not notice any smoke while opening the hood. However we still tried to locate where the smoke could possibly be coming from. While looking under the hood we checked the belts and they seemed fine. However the coolant reservoir is located in the area where we seen the smoke. I open the reservoir and notice the coolant looked muddy. So I figured that the van may just need a radiator flush but when I spoke to a mechanic over the phone about the muddy coolant he said that it may be muddy because the van may have a leak and there could be sealant in the reservoir. Then he replied that if that be the case he would not recommend a flush. From the description that I gave you could someone please tell me where the smoke may be coming from, why my battery light may be on, if you would recommended a coolant flush and why the van may be bucking?