As a starter, I would recommend using the 18-135mm as much as possible to find the focal length you shoot the most. I shoot landscapes using the 18-55mm STM kit lens as it is light and when stopped down to f/5.6-8 it does well, especially with blended images. Sometimes there are recommendations to "get a 35mm" or "50mm is too long" however each photographer is different and it is important to know your own style and then move from your current lens to more specific models.

The photography styles you have chosen can get quite expensive lens wise. Take a look at demo and used lens and you can save quite a fair margin. For example, the 55-250mm STM is relatively high priced as new as it comes in kit form however there are many photographers who are upgrading their gear and selling theirs cheaply.

Third party manufacturers are also great. I use Tamron's 90mm and 70-200mm VC lens and Sigma's 85mm and they are usually half the price of the Canon equivalent while performing only slightly less.

Canon's range and pricing of STM lens is wonderful for the beginner photographer. I use the 50mm f/1.8 STM a lot more now as the focus is more accurate than the older version and it is a light portrait lens to use in low light.

I use eBay for most accessories except for tripods and filters, the latter to avoid fake copies and avoid colour cast. When choosing a tripod, you get what you pay for. A sub-$100 tripod can actually exacerbate vibration and make your images worse. Stick with reputable brands and avoid the budget models and they can last for decades.

I usually just put my camera in a cheap neoprene camerabag and then into a backpack when hiking.

I recommend lens hoods to maximise contrast especailly when shooting on sunny days or with strong light sources in the frame. As a side benefit, it can also protect the front glass element of your lens. There are many cheap third party lens hoods on eBay for most Canon lens.

For straps I use Joby Pro Sling Strap for easy adjustment and long day shooting. I have never used a neck strap due to how uncomfortable they are.