Would like advice on the following?
- What lens to get to do landscape images?
- What lens to get for weather photography?
- Is 450D suitable for HDR?
- Any good bags for this product?
- What filters?
If you want to take mainly landscape shots, then you could look at a super wide angle (SWA) lens such as the Sigma 10-22mm, or the Canon equivalent. It's 50/50 on camera forums usually as to whether the Canon is worth the extra dosh. In fact if anything I would say more people go with the Sigma. On your crop sensor 450d this will give striking wide angle shots.
It depends on your budget as to what you can get, but if you do not want super wide angle, and more just a much better kit lens range, you could look at the Canon 17-40mm L f/4. I have owned this lens and can recommend it. It gives great colour and contrast and also has the benefit of being L glass with high build quality and weather sealing. Having said that the 450d is not a Pro sealed camera is it. But to be honest, it depends how extreme you go in the weather.
Yes 450d is suitable for HDR. Any DSLR is. In fact, you can make a HDR image from one single jpeg although this would not be advised. For best results, shoot in raw format and take 3 or more images at different exposure levels to account for the extremes of the shadows and highlights of the scene. Then in post processing, you can merge them and appply effects for HDR. There are some free apps that are very good at this.
Bags. I recommend Tamrac having owned some of their bags. There is a whole world of different bags. It depends if you want a small backpack, one shoulder bag etc. Light and small, or big and able to carry a laptop and other lenses.
Filters. For landscape photography there are various you can use.
Circular polarizers will come in handy for reducing glare and reflections, and giving dramatic blue skies.
ND (Neutral Density) filters are used for long exposures (not necessarily at night) where say you might want to reduce the light entering the camera to enable a long shutter speed to capture a silky smooth looking waterfall for example.
Graduated ND filters are for when you might shoot a scene at dusk and you want to use a very long exposure again, but use an ND filter to stop the Sky from being overexposed and bring out detail in the foreground for example.
UV filters are just for protection really and there will always be a big debate on whether to use one or not. A lot of people just go with a lens hood as do not want to impair the optics of the expensive lenses they bought, where as others sacrifice image quality and buy a very expensive UV filter to add protection. Cheap UV filters can give nasty lens flares and reflections so do avoid them.
Infrared filters are for infrared photography. That's a whole new topic in itself and you probably won't want to go into that.
It's best to invest in good lenses with SLR ownership. They nearly always hold their value (apart from some newer ef-s lenses where they have been replaced by others in Canons line up) and they can be used on all bodies in the future (apart from EF-S lenses on Full frame cameras if you ever turn more pro and buy a pro body).
Hope this helps.