Bio's are sexy lh3 leechers as well... I should know... I got mine from a bio from an allied guild.
They'll probably make you pay for AD ingreds though... so that's like 2mil + zeny for the leech.
And for your second point, either supply a cloak or hiding clip or ask for one from the leecher. Some leechers might give you one as service (saves them time and using yggs to res you)
Unless you're a sin or rogue... then you should have the skill anyway.
I had 2 leechers, one champ who suffered a lot of lag and a bio who was amazing. If I remember correctly it took about 6 hours total...
but it could be more.. could be less as well...
Though I only went to 99.9% on level 98 though, I wanted to get 99 with the guild there
