Gert Very, welcome to the Forum
Well, we have been to Addo the past 2 years in July and although it is winter rainfall area, we had slight rain now and then, but enjoyed the time there. It is cold in the mornings, so plan accordingly.
According to the Addo brochure, they have 2 peak rainfall times i.e. Feb-March and Oct-Nov. The temperature in July varies between 5 - 18 degrees. You might encounter some warmer days as we have experienced, but also one year we had a rain storm for one day causing flooding in the neighbouring towns.
2. Nice spots/water holes for birding
There is a bird hide in the Main camp and two waterholes which is flood lit in the evening where you can enjoy some ellies and other.
Another bird hide is at Spekboom further down to the south of the park and close to a very nice picnic site (Jack's picnic) with great braai facilities and refreshment areas and a sighting board.
The area where I have spotted some great birds are from the viewpoint looking across the Domkrag dam (Domkrag named after a large tortoise jacking up cars
). I have spotted some interesting birds on Harvey's loop on the southern side of the park as one crosses the central area.
On all the different roads, you will get some birdies and look out on the section past Marion Baree to the south for some Secretary birds. Lots of Black shouldered kites around but lot of activity close to Domkrag waterhole.
3. Nice routes
All the routs are great, and the road in very good condition. Gwarrie Pan has been good for large ellie herds (the elephants are a lot more relaxed than those in Kruger). We spotted some lions and hyena on the road past Marion Baree, but also on Harveys loop and just outside the Main campgate. They also love Carol's rest area with the open plains which host some eland and zebras kudus and all the smaller creatures.
Be careful of the black rhino, they can be temperamental and territorial as I had a bad experience once on the Ngulube loop.
But to give you an idea what to expect, you can have a read:Addo July 2013
Hope this helps.