You're welcome! I'm glad I can help.
Hmm, I wouldn't say that there is a recommended number. A lot of it depends on other decisions you'll be making. Making tiles is a bit like doing a bunch of work upfront so that things are less work down the road. This means that if you're doing a small scale game, only a few locations, not very big maps, then worrying about tiles would probably be more trouble than it's worth, and having a lot of unique things won't be any harder than making tiles. However, if you have big maps or lots of locations, then breaking things down into lego pieces will be very much worth it, and make everything faster.
There is an upper limit when working in RPG Maker. VX, Ace and MV all have a limit of 4 B-E sheets, each with a limit of 256 tiles (except B, you can't use the upper left corner tile, so it has 255 available). There's also the A tiles, but putting unique stuff in there gets a little complicated. The A sheets all have different rules that govern how they get placed on a map, and the only ones that work like other tiles are the ones in the A5 sheet. They're always at the bottom, so it's not the place for anything needing transparency. For Ace and MV you can also have different tilesets for different maps. VX is trickier, I believe it's only one set for the whole game, so you have to choose carefully what's on it. XP doesn't have a limit, since you can just make the sheets longer (there's a lot to love with XP's mapping), but the longer it gets the slower your game is. 2k and 2k3 have one sheet per map, the sheets are tiny, and they have rules for what the different sections on the sheet do. I'm not very familiar with 2k/3 yet, so I don't know a lot about how it works. Anyway, the point I'm trying to make is that while you do have a lot of freedom to use a lot of unique tiles, if you're making a big diverse map you can actually run out of room for everything you need.
There are some alternatives, though, that can free you up quite a bit. There's parallax mapping, where you give up on tiles completely and just make a picture as your map. There are tutorials kicking around for learning how to do that. It's not my thing, but there are others who adore it. Parallax mapping does take up more memory than tiles do, by a significant amount. It's not a big deal if your game is small, but if you have a lot of unique places your players might get upset by how much room your game takes up on their computer. There's also alternative mapping solutions like TileD and Grid Free Doodads, where a plugin/script circumvents the normal mapping and lets you do it a different way.
I like your picture, it's dynamic and interesting, and the space it takes up on screen makes it feel more personal. It reminds me a lot of the old Adventure Games. Too big or too small will depend a lot on your choices, again. If it's a big or small game, if you're going to add in a lot of texture/detail or keep it simple like it is now, stuff like that. If this is the entire map, then you won't have any trouble fitting everything onto sheets.
Pixel art, as an art style, is all about precision. The look of something can change drastically with a change of only one pixel so a lot of care goes in to placing every single pixel. The cool thing is, because of that precision, pixel art can be really sharp and clear even when showing something tiny, unlike raster art where going small means it's too blurry to understand. It's also really great for recoloring. Anyway, that's why bigger scenes aren't recommended, putting that much effort into a whole screen's worth of details can be very exhausting. You might burn out before you get far in game creation. If the style is simple, well, there's not a lot of precision needed for 90% flat colors. A simple style can make it easy enough that going big won't be too much. If you're going to make things complicated with textures and details, then going big becomes a huge amount of work.
For me, I like to be very limited on the tiles I need, making them usable in as many places as possible. No tile is unique, but by placing things differently and using alternative tiles to add variety, I can get some beautiful, almost unnoticeably tiled maps. Doing it this way allows me to make a ton of interesting locations without driving myself crazy with how much work I need to do. Adding a new location is as simple as mapping it. I'm not saying you should do it my way, just wanted to give you more information, make it easier to decide what would be the best for you.
I hope this long winded ramble about tiles helps you come to your own conclusion about if you want to do mostly unique tiles or not. I look forward to seeing what you decide to do and the pretty results of your decision.