Regarding the reservation -
The high travel season is not really considered to be over until after Labor Day when the Americans all head home from Europe.
The seating is always at a premium - but my thought is you have options beyond the Eiffel Tower for a beautiful view (of the Eiffel Tower as well) in Paris should you not be able to obtain seating.
A few examples:
Cafe de l'Homme - at Trocadero - looking directly across at the Eiffel Tower with terrace seating. Next to the Musee de l'Homme.
17 Place du Trocadéro, Musée de l'Homme - Paris XVIe - Tel : +00 33 (0)1 44 05 30 15 - note reservations here too will NOT require a credit card online
Restaurant Georges - Centre George Pompidou -
On Level 6, Restaurant Georges has some of the finest panoramic views of Paris. The work of Dominique Jacob and Brendan McFarlane, its architecture conforms to the centre's novel structure and is decorated with contoured aluminium sheeting.
To book a table :
Telephone: +33 (0)1 44 78 47 99
Fax: +33 (0)1 44 78 48 93
Question 2 - I am wearing light jackets daily. The autumn temperatures have begun as of last week. The air is chilling at night and I have seen a few leaves falling throughout town. The mornings and evenings are cool, while mid-day can be quite lovely. We are have rain every few days or so - so plan for evenings in the mid to lower 50s and days in low 70s.