Because the valve gear bars have a much smaller cross section 
than the rods, the bars are much weaker than the rods. Thus, the 
bars should not be used for heavy lifting. 

While the rods are easy to work with, I do not recommend 
attempting valve gear on your first steam engine MOC, rather, 
wait until your 2nd or 3rd steam engine. And even then, you 
might only want to assemble a portion of the assembly, e.g., 
http://www.eurobricks.com/forum/index.php?showtopic=74662&#entry1414388

The bars come in two varieties: lighter 2mm without a pin cuff, 
and thicker 3mm with a pin cuff. I like the light appearance of 
the 2mm bars but I think the 3mm bars are easier too work with. 
You have the cuff to protect pin heads from hitting the rods 
behind them. You can also flip the 3mm bars over so that you 
have a full 3mm thickness on the pin, again handy in preventing 
unintended conflicts with the rods behind. 

The 1 hole 1 long washers can come in handy to more precisely 
control your spacing when working with the bars.

In any event, I would recommend prototyping your geometry using 
normal technic half beams first, e.g., 
http://www.eurobricks.com/forum/index.php?showtopic=74662&#entry1429346 

Reading the next few posts in that thread you will also find 
some ideas for making eccentric gears.

Finally, a great source for valve gear info can be found here:
http://www.steamlocomotive.com/appliances/valvegear.php