Ultra sonic is for sure the way to go if you have access.
Fox shocks are the most common for F2's and F3's. They can still be found around ebay for $300 ish. That's what I have on my F2 and it works pretty well
Ohlins used to make them for the F3, but I havent seen one in years. Elka probably makes one now that works for the F3, but a new one will cost you $1000.
I have Traxxion cartidges and springs in my F2. A bit more expensive than Race Tech, and probably not worth the added expense.
The focus on suspension is because these bikes dont have much in the way of ground clearance anyway. Put a big guy on stock springs and they have way less than that, and you'll be bottoming out the forks a lot - not great when you are leaned over.
Go back to the stock front tire size if you can - the taller 120/70 actually slows the steering down because your geometery shallows. And, as you noticed, a stock fender will get rubbed in half by a 120/70 when they get hot.
The F3 is maybe the most stable, forgiving chassis Honda ever built. They are way easy to ride fast, especially when setup for the right weight. Still lots of good aftermarket too. Mild cams and flatslide carbs on the track add good horsepower to the mix.