I agree with the others that if you like it, do it. It's easy enough to take it out later. But for valuable works, I'd suggest hanging the work directly on the wall with two D-rings and hooks (it's more secure, and less likely to get knocked to the floor). Some practical things to keep in mind: Ensure the shelving is strong enough to support the weight of the works you intend to display. Groups of glazed works can become very heavy. This also means using the appropriate means of fixing the shelf to the wall, according to what the wall is made of (seek professional advice if you're not sure). The taller the artwork, the deeper the shelf needs to be to allow enough of a lean. If installing above a sofa or dining chairs, check for head clearance. If the shelf is to be installed in a high traffic area (stair well, hallway), consider having a small raised lip along the front of the shelf to prevent the artworks slipping off. All art moves due to vibrations and air movement. Re cleaning glass and frames: NEVER spray glass cleaner or any liquid directly onto the glass because it will get behind the glass and damage the work. Plus, artworks and frames hate chemicals and moisture! Always use a clean, slightly damp cloth - microfibre cloths are great for this. If you must use chemicals, spray the cleaner onto a lint-free cloth just enough to moisten it, then clean the glass.

It can depend on what you have to work with. If you have lots of pictures you can stack them on top of each other like this: or you can level things at the top. You can mix different sizes like this: Another really good idea is to buy two very long display shelves with a lip at the edge. That way you can change things around and as the bottoms are level it looks consistent. I think one unifying factor is a good idea such as different sizes and frames but limited colour, or everything different but levelled at top or bottom.

I found this guide and a few pics for inspo. I'd suggest laying out a pattern using paper or card of different sizes until you are happy with the look then create your gallery wall.

@HU-902064280 its the Safavieh Kate Shag Rug. We got it from Amazon but its available at a lot of retailers. https://www.amazon.co.uk/gp/product/B00PNR2QXE/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1