In order to work with the Lasso 4D Web Data Engine, you will need to purchase 4D Server - either the Standard or Developer edition. Lasso WDE does not work with the stand-alone version of 4th Dimension. You do not need to purchase the 4D Web Extension License (WEL) for this configuration - 4D Server provides 12 concurrent Lasso connections right out of the box (6 per 4D Client license). Also, note that Lasso and your web server must run on a separate computer from 4D Server.
4th Dimension Server - Standard Edition
4th Dimension Server - Developer Edition
(includes Std. Edition plus additional development tools such as the 4D Compiler and 4D Insider).
Standard Pricing Information
Also, you may want to consider our Partner Program which is an essential resource for serious 4th Dimension development efforts.
Using 4D Server you can essentially replace another database with 4D by simply re-creating your database structure inside of 4th Dimension, importing your data, and then changing your LDML tags to point at your 4D Server database. To ease the database conversion chore, take a look at the 4D Assimilator which uses ODBC to recreate a database structure inside 4D and import rows.