I'm not sure I'm looking at this correctly. Can you add labels and pointers?
It looks like you have an S-trap, (center of top pic) which I don't believe is permitted in new work.
What sizes are the pipes? I don't see where you have 3" or larger coming down from the toilet.

Here are the annotated photos.

Comment about S-trap duly noted and forwarded to Mr. Weedy.

Your vent line is not allowed to go downwards. Neither is it allowed to connect in-line with the waste line. You probably need another vent pipe closer to the toilet.
I believe you need an on-site plumber to design this properly for you.

The vents are all sloping up and to the left, the drains down and to the right.

Are you saying the toilet drain line needs to have its own vent?

What you've identified as the toilet vent drops down at the left end, then goes horizontal before going vertical.
That drop to go under the joists is not allowed.

Copied from the late Lazypup's answer to another post-

"The vent pipe must rise vertically from the drain line. There may be no horizontal run of the vent line until it reaches an elevation of 6" above the flood level rim of the highest fixture served by that vent. "

Based on the locations of your fixtures with respect to the drain line exit, I'd suspect that you will need another vent.

You need a qualified plumber to design a DWV system that will pass inspection in your locality.

late Lazypup? Tell me you don't mean literally! He has been very helpful on a couple previous projects.

BTW, in this jurisdiction, permits/inspections aren't required for DIY work on existing houses. That's why I'm seeking help here. I appreciate your comments on the venting.

I take it that horizontal runs, even if gently sloping up, are still considered horizontal runs?

Yes, sadly we were informed several months ago, by a friend of his, that Lazypup passed away. He is missed.

And, yes, a run is still considered horizontal even if gently sloped up.

OK, I went and did some internet research in earnest on vents, and here's the revised setup.

Question:
I'm not sure the tub vent is ok doing an elbow upwards, since it's upstream from the drain. I couldn't find any diagrams that show a vent going like this, so I'm hesitant, but Mr. Weedy argues that it's no different from a T upwards. There's not room to Tee directly up from the drain line, to the right of where the p-trap section turns right into the drain.

So if this isn't kosher, what's an alternative way to vent the tub?

Anything else wrong here?

That toilet drain should be 3" direct to the sewer/cistern/septic, looks to be 2" only, not good, will plug up regularly. Here in Ontario it must be 4" dedicated line without tie ins, don't get me going on that I didn't write the code. Not sure if it is 3" no point of reference.

No "S" trap from the tub, why a "S" trap? Need maximum hydrostatic pressure to make that turn. OK for a dishwasher, washing machine but without additional pressure not good.

After looking at original pics there have been changes made, no? Now I don't see a "S" trap and the toilet drain looks to be 3".

The vent looks fine from here other than it should be 3", it looks like the drain is 3" with a reducing fitting to 2", continue with 3" to the roof.

Off topic, why no plumbing inspection required where you are? Methane gas can be deadly. I don't get it. I have seen some DIY stuff that can be lethal. I could write a book.

I know you are working on a 60K cottage, don't over think this project in my humble opinion. I see your thread on moonscape plaster to smooth, you are going to drive yourself bonkers.

I hope this helps Weedy.

Toilet (and main) drain is/was 3" in both versions. Yes, we removed the S-trap and the horizontal vents.

My research said vents need to be at least 1/2 the diameter of the drain pipe, which would be 1 1/2". Did I misunderstand the code, or is it different in this case for some reason?

Don't know why no permits/inspections. We're in a small town.

And we're not going to touch the moonscape plaster. The Old House folks talked us out of that. :-)

That looks fine to me. I don't think the 90 on to the vent hurts. Because of joist configuration I have run a small run of horizontal (2') without problem before and it's passed code here.

I should add Weedy, my 2" then goes to 3" up and out the roof. I have never seen an 1.5" rubber roof vent boot. I'll tell you what if they are available from where you get your materials from I imagine it may vent

Sometimes a good hardware store clerk knows as much or more about what will work than some plumbers do. Ask your supply guy or gal your pics and the vent size.