as someone who successfully converted an old Pearl Rhythm Traveler into an e-kit (complete with dual-zone snare and Roland TD-6V) - and then promptly sold off everything cos i didn't like the feel - i think i can try to answer some of those questions.
first off, i do think that the TD-20 is a pretty awesome set no matter what stand you may take on the electronic vs. acoustic debate. i had the pleasure of playing a monstrous TD-20 at this guy's house when i bought over his elims a couple years back, and just the staggering amount of customization (changing the diameter AND depth of each drum!) is amazing. i doubt you'll get bored easily on a kit like that.
marc >> last i checked (years ago, hehe), Sinamex has Alesis DM5s for sale. i think they're in the 400+ price range, if i'm not wrong.
i ended up buying a TD-6V module from music123 cos i couldn't find any place here that would sell the module alone (*ahem*sweelee*ahem*). i think it cost S$800+ including shipping (via vpost, cos roland products can't be shipped overseas due to some restrictions).
IMO, don't use the redshot triggers, they're severely overpriced esp when you consider you can get all the parts you need from someplace like sim lim tower (not sim lim square). i think i spent about S$100+ in all my trips there buying various odds and ends.
i bought roland foam cones as spare parts from sweelee at sims drive, but word of warning: they aren't cheap. i think they run about S$12 apiece, if i'm not mistaken. i tried making my own 'cones' with various types of foam i found at home as well as from online hardware stores like
www.mcmaster.com but in the end the roland ones gave me the best response. i bought lots of nifty materials from mcmaster.com, i just wish there was a place in singapore that sold all that. guess we just aren't very DIY people.
trigger diagrams and models can be found all over the net, just search a little. i also paid for a year's membership to electronicdrums.com which was really helpful thanks to the enthusiastic community there. what i did was i got pieces of black acrylic cut to size to use as the cross-bridges to hold the triggers (most other people use aluminium strips, but you'll realise it's easier for a novice like me to drill acrylic than metal).
don't forget rubber tubing (i got it from mcmaster.com) to line your hoops with so you don't get unwanted clacking of sticks - it doesn't affect your rimshot trigger, don't worry, hehe.
the main problem, as someone mentioned before, is the hihat, esp if you go DIY. in the end, after many unsatisfactory attempts building one with parts i could scavenge from sim lim tower, i got another DIY enthusiast to mail me his hihat controller from the US, it's an awesome design and i still have it lying around somewhere, if anyone's interested. it cost me about S$50 including shipping i think.
i still have a thick reference file on anything and everything to do with converting from acoustic to electric somewhere in my house. flam, if you're interested i could try to make a copy for you or smth.
anyway this post is getting too long for its own good. if anyone wants to know more just post here and i'll try to answer.
last word of advice: be prepared to experiment and spend lots on this project, esp if you decide to sell everything in future. i made a loss on the module, had to sell it on ebay for about US$400. but nevertheless, have fun!
edit: added in some cost figures (cos i know that's what you all wanna know!)