According to my plotter charts it's a full buoyed channel up to the harbour in Perth. Having been toying with this for a while & used the highly scientific method of getting out the car & looking at the river at various states of the tide whilst passing the town. If we get there at a high spring tide, it's likely you could PROBABLY get up to & beyond the North Inch under all the bridges, where if you didn't mind hanging around for a few weeks could likely get quite a lot further! Problem might be getting back to the channel if you miss-time it!
Re Launching there are slips that I reckon would be OK for the top half of the tide at both Brouighty Ferry & Tayport (From memory the boat club of the same name in the harbour owns the Tayport one?) All from memory, but the Tayport slip had more free parking and was a LOT easier to get to from main roads
Have a stroll up the river on the google satellite images - they seem to have been taken at low tide & show the channel quite well. (also shows roughly how close you might get to the railway bridge in Perth at a mid tide!)
And we might be able to wave at Davie on the way past!