Most of the maps you linked are hand-drawn stuff - some digitally hand-drawn, but even so. The first one is of course by one of our own, that's ThomasR's Valtoria. I know he works digitally and with Photoshop, as far as I know. I don't think he ever posted a WIP for Valtoria, but he does have some maps he's been working on that he has shared his progress with, like this one for instance. If you want to spy on him a little and see what kind of steps he's taken to make a map. The middle two I'm not familiar with... The last one, I'm fairly certain is Fransesca Baerald's work. She works with actual inks and watercolours, so there is a good reason why her maps have that certain watercolour wibe.

The reason why I am pointing out the hand-drawn nature of these example maps: while digital work does offer some ways to work around it, very often in order to really get something to truly look like it was drawn by hand is... well, to draw it by hand. Most of us who do the antique/fantasy style maps with digital tools, use a drawing tablet of some kind and freehand many of the things we do.

Now, that being said, there are a lot of ways to produce a nice stylized map without that. I'd maybe check out this series by Jezelf, part 3 in particular. It's a bit outdated at some points, but he does have some pretty good ideas that still hold a lot of merit.

In digital work, a large chunk of the authenticity (in my opinion at least) comes from the usage of paper textures. I don't really know of any good in-depth tutorials in this department, and quite frankly as it's something I've spent a long time working at, I've been meaning to put one together myself... But this little tutorial by Jonathan Roberts gives some idea on how to potentially approach the subject. Plenty of good things on that site in general, so do take a look around there if you haven't already.

As for your drawn elements, there are many tools available even if sitting down and drawing sixteen hundred mountains freehand is not your cup of tea. You can do some pretty awesome stuff with pre-made brush-sets. In this department I cannot recommend K. M. Alexander's stuff enough. He has several sets available, and he's also done tutorials for using them just in case you're not familiar with this kind of work. Check out his blog, it's awesome! The Guild also has a long running thread for mapping symbols that maybe worth checking out, even if some of the links may be old enough to leave to some dead-ends.

Now, this is all just some general stuff on the top of my head. If you could give me any more information, I might be able to give some further pointers. What software are you planning on using, and what is your skill level with said software? Could you maybe share some examples of the map you currently do have and are looking to make a different version of?