Welcome to Astrophotography!
Since you have already purchased your 'scope, I think you should definitely go ahead and try to photograph some planets.
Your results will not be as good as you might hope since as @chili555 points out planets are small, but if you keep an eye on their distances and shoot when they are near their closest distances to Earth, you may have some reasonably interesting results.
You can certainly look for additional things like Jupiter's Galilean moons and their nightly changes, and Saturn's rings, and play with RAW format images and color processing to try to bring out a few bands of clouds, try enhancing color differences for example.
You can also start looking for planetary occultations of stars (ask about that in a new question) or a conjunction between a planet and a star.
And you can amaze yourself by how Venus changes from a small full circle to a large thin crescent while at the same time [managing to maintain an almost constant visual magnitude!
You can also try to photograph a planet or star during the day just for fun
or "video tape" a lunar occultation of a planet
So I'd say go for it! and learn a lot about astrophotography and about astronomy, how to predict things, find them and photograph them, and dream about what your next system will be like if you want to go the route of a much longer focal length and lucky imaging.
About your camera Wikipedia says:
The EOS 400D, called Digital Rebel XTi in North America and EOS Kiss Digital X in Japan, is an entry-level digital single-lens reflex camera introduced by Canon on 24 August 2006.
and
- 22.2 mm × 14.8 mm
- 3,888 × 2,592 pixels
which means the pixel spacing is about 5.7 microns or 0.0057 mm.
Your linked page William Optics Guide Star 61 Guidescope - Gold - M-GS61-GD says that your scope has a focal length of 360 mm.
That means your pixel spacing is 0.0057 / 360 radians or 3.3 arc seconds.
The angular sizes of some planets are
Object angular size image size
(arcseconds) (pixels)
------- ------------ ----------
Jupiter 30 to 50 9 to 15
Venus 10 to 66 3 to 18
Saturn 15 to 20 4.5 to 6
Mars 3.5 to 25 1 to 7.6
With an aperture diameter of 61 mm the diffraction limit at a mid-range wavelength $\lambda$ of 550 nm will be 1.1 $\times 10^{-5}$ radians or 2.3 arc seconds so that will contribute a little but not too much additional blurring considering your pixel size is 3.3. arcseconds, but it means that there's only so much benefit to using a longer focal length with this aperture.
Perhaps doubling it will be worth it, but any more than that will be empty magnification unless you get a scope with a larger aperture.
Of course above about 15 cm astronomical seeing will limit your resolution if just taking snapshots, but with work and some software you can try your hand at lucky imaging.
There are other questions and answers both here in Astronomy SE tagged with photography and in Photography SE tagged with astrophotography that address these topics further.
from How (the heck) was this photo of Venus at inferior conjunction (between us and the Sun) taken? which got it from this answer to Planets visible at night which got it from Wikimedia's File:Phases Venus
These images are beautiful. According to the answer there they were taken by an experience amateur using
- 4.5-inch (Newtonian?) Mizar telescope
- Nikon Coolpix 750
I don't know the exact specs but with an aperture 114 mm and assuming an f/8 Newtonian, the focal length would be 912 mm and with the Coolpix' sensor' pixel spacing of about 5.97 microns that's 1.35 arcseconds per pixel.
