If its your first, I would recommend going with the Ashida for now as its very straight forward with plenty of community support via worklogs. Granted the most difficult part of any portable is the Wii wiring which will basically be the same whichever route you go. Having the other parts all dialed in will minimize the learning curve and headaches of tracking down troubles in a custom build.
But yes, Study the trimming guide and the gboy manual. Read worklogs, practice soldering/desoldering on spare components/boards, take your time and dont be afraid to ask questions if you're having trouble understanding any of the written out steps... you'll get the best response if its obvious you've put in a good try before seeking answers from the community pool.
Good luck!!
