Finishing MDF "Plank" work surface with hardboard?

[Anduril]

I'm about to build a general purpose bench/table for my garage. I'm using reclaimed materials from my late father's massive custom installed book shelves!!! So I have loads of 2x1 and lengths of 20mm MDF (19.5cm x 117cm) (all with pre-existing screw holes of course!).

The top will be three planks of this MDF screwed/glued to a frame (so 58.5x117) and end glued together. I also have an old sheet of hardboard which I plan to cut to size and attach to the top to create a smooth surface.

A couple of questions:

1) What's the best way to attack the hardboard to the MDF: glue it or nail it?

2) What's the best way to seal/paint the hardboard surface (shiny side)? It has an old stain of not sure what (which I'll clean over but will probably still leave a mark). What kind of finish will give a good tough coat. Presumably a primer and paint, but do I need to use a specialist/expensive primer like Zinsser BIn (or 1-2-3) or can I use a general purpose wood primer?

Any help much appreciated.

[wtnhighlander]

I would glue the hardboard to the MDF. My experience with screws or nails in MDF has been less than impressive.

If you can acquire it, I would suggest gluing on a sheet of high-pressure laminate (well-known brand us 'Formica'), rather than paint. Far more durable. But for paint, I might scuff the shiny hardboard first. I like General Finishes 'Milk Paint', it is actually a very tough mineral acrylic. Then top-coat with General Finishes High Performance polyurathane. The top coat isn't strictly necessary, but provides even more durability, and IMO, a better tactile feel.

[Coop]

I did basically the same as you are advocating but used 3/4 ply instead of mdf and used screws to hold the hardboard to the ply. My thought with the screws was to easily replace the hardboard when needed. That was 6 years ago and as I’m not a heavy handtool/chisel user, it’s none the worse today. To do over again, I would probably do as @wtnhighlandersuggest and glue it, maybe with contact cement. 

[Anduril]

Thanks for the input.

On the Finish question, I also won't be hammering on it so Formica may be OTT unless I can find some cheap locally! The paint you recommend looks good, but more than I'd like to spend. (I'm trying to do this as low cost as possible.) 

@Coop did you add any finish to the hardboard or leave as is?

You mention contact cement - is this the same as contact adhesive such as Evo Stik Impact?

[wtnhighlander]

Paint is fine, but stay away from any Latex stuff. It isn't very durable for a table-top surface. That's why I suggested the mineral acrylic.

[Coop]

I applied a couple of coats of sanding sealer on mine. It helps with glue clean up and also doesn’t leave a real slippery surface. 

I’m not familiar with Evo Stik but I’ve used the Weldwood Contact Cement. Apply it with a short nap cheap roller to both surfaces and let them dry. Lay dowels or thin strips of wood on top of your bench and lay the hard board on top of these strips, not allowing contact to the bench because once the two surfaces touch, it ain’t going anywhere. Once you have the hardboard aligned, start removing the strips, working from one end to the other. Use a J roller or something similar (using downward pressure on a small piece of 2x will work) to insure good contact across the surface. If you have a router, you can cut the hardboard a smidge too large and use a flush trim bit to trim the edges after it’s in place.