I already have Tourist Visa, now i don't have to worry about anything for next 5 years unless something change, i can use visa on arrival also but that can change to ETA or something else...Less stress on other stuff is good for my work... in my line of work always have back plans.....
downloadable visa from the site is valid, make sure you print it out to show at the immigration, i wouldn't worry about resending in email because it will be the same as it is on there site....
Yes, once you get your 5 years DTV visa you can use it anytime after that, remember your visa will be valid from the time it issue and not from the day you will arrive in thailand....
if you somehow upload many files then how would they know which one is first and which one last, you dont expect them to sit and sort all the 52 files out for you??? just because its thailand do not think they are the only one does that, i had worst experience with many european countries compare to thailand....have patience and do it proper way and it will help you in your application...use pdfgear