Also keep in mind that the Imperials already had a presence on Tatooine.. it would not be surprising that they kept at least a small contingent of troops after ANH.

If you were to add the SD there, I would probably keep it at one, or just even have a handfull of TIEs; not so much to engage and have a space battle, but they see the Falcon and X-wing from a distance, report in, the report gets to Vader and leads to the DS2 reveal scene, with Vader knowing of Luke's plans, as he is having Luke shadowed (Vader would be smart enough to know that eventually Luke would go to save his friend Han from Jabba, and being that Luke came from Tatooine to begin with, it would be no different than cops staking out a criminal's parents or girlfriend's home).

I would still cut out Vader's arrival in the beginning altogether, since it is redundant as we see the DS2 and have a shuttle land in a DS docking bay when the Emperor arrives.

You could progess as follows:
(1) drop down from scroll into Dagobah atmosphere to swamp surface. Maybe take a training scene from EMPIRE and replace/recolor Luke's fatigues to black and add him chopping something with his lightsabre during one of his backflips. He goes to Yoda's hut and the conversation ends with Yoda dying. Luke goes out to the X-wing preparing to leave.

(2) cut Obi-wan's scene here and either do a top-down vertical swipe or have the camera move down from space to surface of Tatooine with the droids approaching Jabba's palace, where more or less the film continues as it does originally. Whether or not Obi's scene is redone to be at his old hut or not would be up to editor. Personally, I like someone else's idea that once Yoda dies, Luke is on his own with no pep talk or anything until his final confrontation with Vader. That would make Luke's speech later with Leia something that he has figured out through the Force as opposed to Obi-Wan simply telling him flat out.

(3) when they leave Tatooine, have the camera linger as we see the X-wing and Falcon leave (would probably have to alter the FX to show them leaving in formation as opposed to splitting up). As they do a hyperspace jump, we hear and then see 2 or 4 TIEs fly overhead and we hear one of the pilots sending in a message on a coded channel. This segways to Vader, who could be seen pressing a button on his chest plate to indicate that he is the only one getting the message (I would assume that helmet has headphones in it), which then goes to him and the Emperor leaving in said shuttle to the DS2 and thus moving us to the B plot.