Gesso

So my esteemed friends. I have taken Robert Jones' kind advise and I am now the proud owner of a range of chromacolours, and a few interactive acrylics. All new to me. I tried a couple of quick and rough (very rough) sketches on paper, just to see the pretty colours. While I like what you can do with the paints, not too happy on paper, so I paid a visit to my local hardware store and picked up a few off cuts. Excellent value by the way! 50p for two foot square. Mixture of hardboard and heavier, 10mm MDF, so I can see what I like best. Now - I'm new to acrylics, having only ever used watercolours. I know I have to seal the boards with gesso. So I bought some (ouch - thats expensive stuff!!), and I've just put a (first?) coat on a couple of boards. And here I start to fall over.......................... The gesso is , very thick. Impossible to get a nice neat coat, but at least I covered the boards. And the wall. And Ok, maybe a bit of carpet.................... And the nice new Christmas jumper might have to be washed off ......a bit. Questions!! Is there a (cheaper) alternative to gesso? Failing that, can the gesso be watered down slightly, making it easier to use without losing its adhesive properties? Do I need two coats (or maybe three)? Is it best to sand down to a smooth finish, or is it OK to leave a bit of texture (I favour land/waterscapes by the way). I'm sure I will think of more quetions even before I log off, but thats a pretty good start! And all this before I've dipped my brush.............so to speak........... Thanks in advance.