The combination of automation tools that LenoxSoft should use to achieve their goal is an automation rule and a completion action. An automation rule is a rule that runs continuously in the background and matches prospects based on the criteria you set. A completion action is an action that Marketing Cloud Account Engagement executes after a prospect successfully completes a desired activity, such as submitting a form or clicking a custom link1. LenoxSoft can use an automation rule to update the custom field for anyone who has submitted the form before today, and a completion action to update the custom field for anyone who submits the form moving forward.

Explanation
A new automation rule does not require any additional action for prospects to begin matching that automation rule, other than saving the rule. Automation rules are active by default once they are saved, and they run every hour to match prospects based on the rule criteria. Resuming, scheduling, or previewing the rule are not actions that are required for prospects to begin matching the rule, but they are optional features that can be used to manage or test the rule. References Automation Rules Overview

Explanation
According to the [Salesforce documentation], when a new lead record is created in Salesforce without an email address, and the Salesforce connector is set to automatically create prospects in Marketing Cloud Account Engagement, no new record will be created in Marketing Cloud Account Engagement. This is because email address is a required field for creating a prospect in Marketing Cloud Account Engagement, and without it, the lead record cannot be synced or matched with a prospect record. A visitor record is created only when a person visits a tracked web page, not when a lead record is created in Salesforce. A new account will not be created either, as accounts are synced from Salesforce to Marketing Cloud Account Engagement based on the account ID of the associated lead or contact record. A new prospect record will not be created, as explained above.
References: [Salesforce documentation]

Explanation
A good way in Salesforce to verify that a record is syncing to a prospect in Marketing Cloud Account Engagement is to check that the Marketing Cloud Account Engagement URL field is not empty. The Marketing Cloud Account Engagement URL field is a custom field that is added to the lead or contact object in Salesforce when you connect your Marketing Cloud Account Engagement account with your Salesforce CRM. The Marketing Cloud Account Engagement URL field contains the link to the prospect record in Marketing Cloud Account Engagement that corresponds to the lead or contact record in Salesforce. The Marketing Cloud Account Engagement URL field is populated when a prospect record is synced from Marketing Cloud Account Engagement to Salesforce, or when a lead or contact record is synced from Salesforce to Marketing Cloud Account Engagement. Therefore, if the Marketing Cloud Account Engagement URL field is not empty, it means that the record is syncing to a prospect in Marketing Cloud Account Engagement.

If LenoxSoft has a Marketing Cloud Account Engagement form titled "Request a Demo" on their external website, they should use the Form Report to see how many views their form has received (D). The Form Report shows the number of views, submissions, and conversions for each form created in Marketing Cloud Account Engagement. The Conversions Report (A) shows the number of prospects who converted from anonymous visitors to identified prospects. The Landing Page Report (B) shows the number of views, submissions, and conversions for each landing page created in Marketing Cloud Account Engagement. The Form Handler Report shows the number of submissions and conversions for each form handler created in Marketing Cloud Account Engagement. References: Account Engagement Campaign Reporting