How to convert my lotus 2000r into a single speed
You should get away with the new freewheel by itself, simply take the freewheel off the current wheel and fit that.

You will need a chain tool to shorten your chain, and depending on the dropouts you may need a chain tensioner, or you might be lucky.

Note that while you don't need new chainrings, you won't be able to shift front gear without either a chain tensioning arm, or leaving the rear derailleur in place, to take up the slack.