Okonoyamiyaki

Hmmmmmm I'm not too fussed about cleaning as long as it's not specifically bad. Like I don't mind it when sound effects aren't done (although I tend to translate them all when I do my own translations.) 
When it comes to outside bubble-text (non sound effects) it's best if it can look as close to the original as possible. That's hard on the redrawers, but otherwise it can end up being kind of distracting and when it's like a pivotal plot moment that can ruin the atmosphere. If redrawing is hanging up a release for weeks though, it doesn't need to be the most perfect ever. In the end, this is fan work and I don't think anyone would get really upset about it.

Watermarks I'm not too sure about, but if they're in the way, yeah.

Ah, along these lines though, I do have preferences for typesetting. I cannot stand vertical typesetting in English, it's almost impossible to read. Like, if it's absolutely necessary, turn it sideways (like you'd see on the spine of a book or movie) if you must. Otherwise just keep make it as thin as possible. Reading vertically in English is the biggest pain the the ass.
This mostly happens to like, battle cries and names of special moves but UGH.

Also gratuitous splicing of words, like when it doesn't fit and the typesetter does something like:
"I'm go-
ing to
save
the wor-
ld !!!"

No. Pick a smaller font or break it up better. D8

"I'm
going
to save
the
world
!!!"

Is just fine.

There is no excuse for that. Super gets in the way when reading. Like, it's unavoidable sometimes for legitimately long words but about 90% of the time it can be fixed if the perimeters are changed a bit.
Also not huge on lots of different font changes based on a typesetter's interpretation of the script when there wasn't a change in the original. Like, "I feel this person is probably speaking softly so I'll go with a curly font" is kind of forcing their interpretation on the reader. If it's something that's chosen to reflect the original manga's font change, it's awesome but I've seen a few where it was sort of more artistic interpretation. As it is, we already have the manga painted over slightly with the translator's brush no matter how objective we try to stay.

For me it would depend on the series. I'm a fan of marathoning (I'll often even go back and read a favorite series all at once,) but if it's a series that's currently being serialized in a magazine, I'd prefer not to wait if I don't have to. Like having to wait for monthly titles already can be painful.
Weeklies I wouldn't mind saving 1 to 3 of at once because like, honestly they're already really short releases and by the time I get into it, it's over.

For older things that are being scanslated with the tankouban though, bulk...ier releases (a couple chapters) is kind of nice. I agree that more than a few chapters  at once though can be kind of daunting and may mean that it gets moved to a backburner. Like more than 4 or 5 at once is like, "Oh I guess I'll do this after I read the shorter releases..."
I follow several...Uh... Hundred (?Too Many. Not Sure) current series so even if I read everyday, huge bulk releases might mean I get distracted or wander away in the middle.
I kind of like the idea of 2-3 chapters the most. Enough to get into it and excited but not so many I'm like "Gyaugh I have other things to read."

Either way as long as it doesn't just sit there for more than a few months without updates, I'm pretty happy. After 4 or 5 months, I end up not really being able to remember what was going on so even if there's a bulk release of like, a zillion chapters, it's a pain since I'll have to go back and remind myself. That's kind of demotivational at that point.

As far as text goes, I read both really long-winded wordy ones and really simple mostly fighting grunty ones. If it's interesting it doesn't really matter. For the ones without much text though, because they go so fast, I find one chapter releases kind of underwhelming and forgettable. I've found I'll often have to re-read a past chapter for context - especially the weekly JUMP type series. Contrarily, if it's a really wordy one and there's a huge bulk release, it might be harder to get through it in one sitting so it might sit on a side tab for a few weeks. 
 

Hmmm.... This kinda sounds like it could be Arata Kangatari? Also maybe not though. >< I don't think anyone other than the Aratas went over to the other worlds....
http://vatoto.com/comic/_/comics/arata-kangatari-r1790
I hope this helps!
Body switching/parallel universe manga are everywhere so it could be a lot of things....

As far as historical manga goes, There's the really aptly named....

Historie (Same author as Kiseiju) so you know it's awesome: http://vatoto.com/comic/_/comics/historie-r1214

Vinland Saga because more Vikings are always a good idea: http://vatoto.com/comic/_/comics/vinland-saga-r350

Shut Hell because omgshutup Tagnut Empire manga is rare as hell, that's my favorite empire no one knows about and also why not add some time slipping reincarnation elements, sure: http://vatoto.com/comic/_/comics/shut-hell-r2453
(There was also another more fantasy-ish fall-of-Tagnut-Empire meets painting manhua that toed the line of ridiculous but was still enjoyable called Painting Warriors: http://vatoto.com/comic/_/comics/painting-warriors-r2764  if you're interested in Tagnutty Goodness.)

Otoyomegatari. Sadly, the early chapters aren't on this site anymore.

^ I very much second this because Kaoru Mori's attention to detail and love of research is second to none. Her door carving double-page spread in like the third chapter of this literally made my cry the most manly of tears. Like seriously, this is hands down the best thing. Like omg how long does it take to draw the... Everything. My god.

Her earlier series, Emma, is also fantastic: http://vatoto.com/comic/_/comics/emma-r1016

The chapters are no longer available here (official releases yay) but not only the manga's content itself but also the liner notes in Thermae Romae are hella detailed. There's an amazing amount of information between the hilarity and manly tears: http://vatoto.com/comic/_/comics/thermae-romae-r1017

Recently I'm enjoying the heck out of Gold Kamui http://vatoto.com/comic/_/comics/golden-kamui-r16663 because Ainu stuff is cool and it covers bits of the Russio-Japanese war. It's mostly a historical setting and not so much about actual history but it's awesome so let's go with it, sure.

Hmmm, I think the first one is probably http://vatoto.com/comic/_/comics/shoujo-shounen-gakkyuudan-r10484

I hope that helps!