I try to not get caught up in 'this will make my work less mine', it will prevent you eventually from advancing to larger forms of creation. If you publish professionally, someone else will be involved, many pro comics have the art split up into teams... the inker won't be doing the logo. If you make a movie or game, hundreds and thousands of people will be involved. Getting over the 'it's not purely mine' headspace is vital if you want to get to larger forms of creating.
My work is now in hundreds of people's books because they were great writers but not cartographers (as I'm sure some of you know I ended up stumbling into becoming a
professional fantasy cartographer which is working out financially far better than comics ever did for me x_x). Their novel is no less their novel just because it's supported with my art. I view this as the addition of harmony to a melody. Eventually with enough people you will have a full symphony. If you just want to be a guy on a street corner with one guitar and you don't aspire to be a symphony, then cool.
At some point I had to jump over the ravine of 'but I want my art to be MY art' and accept that I was now a conduit for someone else's ideas if I wanted to get paid, and consider how that worked with my vision of "being an artist". It's still my world map painting even if someone else sketched it; it's still their world setting even if I drew it. We collaborated. We harmonized. We made something bigger than we could have if we limited ourselves to doing it all alone and forced ourselves to learn to do it all for the sake of our pride.
Thus, your comic is no less your comic just because you supported it with a commissioned outfit design, logo design, web design, an inker, a 3D modeller who does accurate castle backgrounds for you to draw over, a flat colorer, a full colorer, buying a font, buying stock art to use as backgrounds, buying stock models to use as items in a scene... just, the more you involve people in the project the more you need to communicate with them to make sure they're clear on what you're doing with their contributions, and if / how they will be credited, etc.
Some of creating is conducting skill from multiple sources to come together and make a better quilt than you could have alone. Moving from indie into big money making creativity makes this skill vital. The biggest projects I've worked on involved dozens of people doing different kinds of art... and those people are likely also standing on top of the work of other people's brushes, stock textures, fonts, programs... on mythological tropes and tales as old as time. I have come to believe creativity is contribution to a co-creative multiverse. There is no purity. In some way you have already been influenced.
If what stands between you and a great comic is your lack of knowledge of how exactly castles function, then go forth, use a 3D model, a photograph, or hire a background artist. Or go learn about how castles function and draw hundreds of them until you're satisfied if it chafes you because you think you should be able to do it. All of these ways are valid. The only major concern I would have is the rights to using said castle model, and that's when a good conversation or contract will come in handy. Keep in touch with your collaborators so there are no unpleasant surprises.