Freewheel to cassette Conversion 2016 Windsor Wellington 2.0 I am a fit but heavy rider. I am looking to change out my stock wheel set on my Windsor Wellington 2.0 (Bikes Direct.com) to a Veulta HD 36 700c spoke wheelset. I'm just wondering and hoping my Shimano Tourney 3x7 drivetrain will accommodate a 7 speed cassette on the Vuleta Wheelset. Does a spacer avoid the need to make any modification to the drive train? Do I need a different chain?
Thank so much for the advice!
Wheels with free hub bodies for 8 to 10 speed cassettes can accommodate a 7 speed cassette with a readily available spacer. 

Your bike almost certainly has standard road bike 130mm dropout spacing, but it’s a good idea to check before purchasing s new wheel. 

Derailleur should work fine, will probably need limits reset and indexing adjusting. 

It’s a good idea to get a new chain with a new cassette. A worn chain will accelerate wear on a cassette.