For SL1 not really, no. Most resources available are on the speedsouls wiki, otherwise your best bet is just watching runs and following along - feel free to join the speedsouls discord for more help as that's where the most people are active.

I had no issues with gadget or livesplit, but I suppose it depends where you get the game from.

The reason people do it that way is because ancient wyvern and yhorm don't require you to have any damage; the bosses are ordered in the fastest way possible (where applicable). If you want to do it a different way, no, that is not a "problem" but keep in mind you will be doing yourself a disservice in terms of speed