There's a limit (70) to the number of form fields you can have on a custom list form. Does anyone know what this count includes? I am wondering whether I can stay under the limit by replacing some editable fields with xsl:value-of or by setting the FormField's ControlMode to "Display". There are some items that need to be shown on the edit form but not actually edited.
70 fields on one form does not sound like a great user experience. You may want to re-think your data architecture.
Other discussions show that exceeding the limit will result in a stack overflow error. Even a field that is just displayed would need to be on the stack, so the display mode will probably not help much.
In any case, why don't your try it out yourself? Create some data in an Excel file and import that as a list, edit the form with SP Designer and see what works and what doesn't.
InfoPath does not have this limitation, so customizing the form with IP is an alternative. You can then also use a tabbed interface to improve the UX.
You really don't want to throw a page with 70 fields at a user.
Edit: With the information provided in the comments it seems that you have a parent/child (or master/detail) relationship and try to pack it all into one list instead of building a normalized database structure. Parent/child relationships can be set up in SharePoint, too. You don't need to create dozens of fields to store the detail data for a master record.
If you go through the material (the 2007 stuff is good to understand the approach), you'll find that there are two techniques, one using SharePoint Designer, the other one without SPD.
It is entirely doable to create relationships to several different detail lists, if required.
There is a limit of 70 fields (67 fields plus one attachment field, one created by field and one modified by field) on custom forms. The limit can be overcome by instead customizing a list form with an InfoPath 2010 form.
I think use the InfoPath form But I think time to redesign the form in different tool Access / SQL as InfoPath is also retiring.