Migration from D7 questions

You might find this helpful:
https://forum.backdropcms.org/forum/virtual-user-group-migrations

Also, if you have ideas on how to make the migration better, please post them here:
https://github.com/backdrop/backdrop-issues/issues/3578

#2) I've done one D7 to Backdrop CMS upgrade and I believe that MetaTags updated pretty successfully. I think that Webform should also upgrade pretty smoothly, but I have not done so myself yet. 

#4) You can post a "port request" here. Sometimes someone with experience will help port a simple module pretty quickly. You can also check this page to see if others have been asking about a particular module or to add your interest to an existing port request. https://github.com/backdrop-ops/contrib/issues

Hopefully, others can chime in and provide answers to some of your other questions. 

I assume node references migrate well!

If you are using the references module in Drupal 7 then yes, the Backdrop version is identical. We are also working on a new Reference module, which will be a little different (more like entity_reference for Drupal 7) but we will also provide an upgrade path from references when it is ready.

1. We used a ton of Views. Most pages are collections of View blocks. What kinds of fields or formats will not migrate (aside from php fields, which I will need)?

Anything that was in the views module itself in Drupal 7 is in Backdrop core. Anything that was an add-on module, will also likely need the same module for Backdrop.  You'll be happy to learn that all your views themselves should convert over automatically!

2. Will Metatags migrate fully?

Every Metatag sub-module that is supported in Backdrop has an upgrade path. I'd check to see which you are using on your D7 site. If there's something you need that's missing, ask for it in the queue.

Webform?

There is also an upgrade path for Webform. The only issue I remember is around the access by role, since the user roles names have changed from '0' to 'anonymous' and '1' to 'authenitcated'. (On closer inspection, this has since been fixed).

3. What system does Backdrop use to build a View Google map of geocoded locations in nodes?

I know that Geofield for Backdrop includes a google map display for views that works pretty well. I expect there may be some other options as well.

4. Modules I think I really need that I have not found: Cookie Crumbs, Login error, Imagecache Canvas Actions, Local Menu. Are there other ways to do these things? If not, these are probably easy to convert, but thought I'd ask if there are existing options of a different name.

Cookie Crumbs should be a quick one to port. Maybe even a good candidate for your first Backdrop port! ;)

My primary use of Imagecache Canvas Actions for Drupal 7 was to make a white background on a resized image, instead of black. That has been fixed in Backdrop. What are you using it for?

Local Menu may be reproducible with Backdrop's core Menu blocks, as they are more like menu_block module now, which looks similar.

I could not find a drupal module called `Login error`. Could you please provide a link?

Are the ids and classes from Views the same once we get past the node and page changes documented for converting themes?

Yes, the views output is nearly identical.

Lastly, how do I go about estimating hours for this conversion?

This is the hard question, isn't it?

I usually estimate at least 8 hours for running the update itself. This gives me a chance to run the whole thing at least twice. The first time I know will be a throw-away upgrade where I can test everything. Then I start over, doing everything in the correct order, and with all the missing pieces in place. :)

I've kept some notes on my various upgrades, which you might find helpful.

I usually estimate time for module ports around 2-8 hours each - for reasonably sized modules. Large or complicated modules take longer (but the longest I've ever spent on a module port was 2 weeks).

The theme conversion / layout builds will depend on the complexity your current theme.

Beyond that, the "extra" depends greatly on the complexity of your site. I've had this end up being nothing in some cases, and weeks in others. 

my client is pretty tolerant of time ranges, but I'm not sure just what I will run into after I do the actual conversion.

Can you ask your client for a ~4-hour budget to run the update, and see?

If you exclude the modules you know need to be ported, and leave the upgraded site in the default Backdrop theme (Basis) you should be able to click around the rest of the and see what's missing.

Then you can bring those things back here and maybe we can help you get a little closer?

not login error, it's custom error

The customerror module also looks like one that will be straightforward to port.

Open Graph tags for their Facebook posts

Great! That submodule is already ported :)

I just heard that Imagecache Canvas Actions has been ported, but it is now called Image Effects: https://backdropcms.org/project/image_effects