SAP Transaction code to pre-compile all system program

If I have to run SGEN and have to recycle the server as well for clearing out memory, does it make sense to run SGEN first and recycle afterwards, because SGEN will sort of litter the memory or is it inconsequential what runs first.

SGEN is ued to "compile" ABAP programs. Results are put in database.

So, if you restart SAP, compiled results will still be in the database, so, no need to run SGEN again.

Make use of the transaction 'SGEN' to re-generate all the SAP programs after you change version of your SAP kernel, upgrade SAP system or apply support packages.

Do take care of the table spaces and use SAPDBA to observe them.

Do it during a weekend which is the best or a period of time with very very low users activity.

It will takes about 5 to 8 hours depending on the type of hardware configuration you are using.