Yamaha DTXpress/DTXplorer/DTXtreme

I just purchased the rack and pads of the DTXPress III...Now that 
I've done this I half wish I hadn't...here's my questions...

1)If I get a roland module, will I need to purchase an FD-7 for the 
hi-hat? or can I purchase an inverter somewhere to reverse the 
polarity?

2)If I get a roland module will my pads respond and trigger as well 
as if I were using the yamaha module?

3)If I get a yamaha module, what is the difference between the 
dtxpress II module and the dtxpress III module?

4)I'm mainly wanting to use this for midi to trigger samples on 
native instruments battery...so my questions, is there a more 
inexpensive module I can purchase without sacrificing the use of the 
hi-hat?

I'd appreciate any help as I'm quite a bind right at the moment.  I 
spent a little much for this, and I'm a little tight on the funds at 
the moment.  

Thanks, shawn