DWI - how DSA would affect my VISA status (G4) and future VISA applications

You should be represented by a criminal defense attorney who handles these cases regularly. If this is a first offense, then often times the matter can be handled without you having to enter a guilty plea. Whether or not you plead guilty, you will have to disclose the charge and disposition on all future visa applications. Additionally, if you are placed on probation, you may need permission to travel, each time you travel which can be extremely inconvenient for G-4 visa holders since G-4's often spend a great amount of time travelling.

Whatever you do, whatever the outcome, I would not get the record expunged (later) unless you have consulted with an immigration attorney. USCIS will require you to provide a certified copy of any charges and/or dispositions at each stage of your immigration history and it can be very difficult to obtain once the record is expunged.