For the purpose you describe they are perfect and will reward your efforts accordingly.
Trigger wise all you need is here.... http://www.airgunbbs.com/archive/ind.../t-370681.html
(the 'postfromspain' website has gone but the description is there...
Velocity wise I'm not aware of much that can be done either easily or cheaply, there used to be a description of how to do something, but it involved hot glue and it all looked a bit of a bodge IIRC