For the past 3 years I have been consistently working solo in my free time (I am a programmer) on a space game that can be described with the following keywords:

3d top down, desktop, single player, space, real time, open-world, combat, exploration, missions, trading

The stage of my game which I consider in pre-alpha is the following:

1. prototype ready and playable
2. core gameplay concepts and mechanics are complete and implemented
3. 3d models (spaceships, planets) and effects (i.e. explosions) from the store (the models are good though)
4. core ui concept implemented with some programming ui art (the art will almost certainly change later)
5. some sfxs (i.e. explosions and ui sfxs)
6. No title yet

Certainly the project is far from completion but I was thinking whether it is now the right time to start showing my work,
draw some attention and maybe get some help, but not sure where to start and what to do since there is a lack of experience
on these aspects of development.

I was thinking the following:

1. dedicated Web site with forum, wiki to expose the details of the gameplay show screenshots etc
2. reddit
3. videos on youtube with updates

however I am concerned whether those side projects (especially the web site) are going to draw significant amount of time
from the actual game development.

The typical guideline in the professional world is that main development of a game is about 1/3 of the total cost.  Another 1/3 is spent in marketing, and the rest is spent in pre-production, post-production, and other tasks. Actual numbers vary, but I've seen that number used on many games from many studios.

Yes, marketing takes time, and usually costs money.

With that same ratio, you would spend the next three years dedicated to marketing, just as you spent three years in development. You can pay people to help reduce the time you personally invest, time and money are exchangeable.

There's an old article on the site's archive that also applies. The advice is still solid after 15 years.

Thank you for your answer,

the article seems very interesting, however one thing that still is not clear to me is which is the optimum development stage for starting to advertise a game and more specifically for a game as described in my first post.

moreover before paying someone for marketing I would like first to get some feedback from people that are interested in this particular genre and which would be the best platform to do it, but first it seems reasonable to show some of my work (main screens and videos) and for that I am thinking of making a website.

All of those are part of marketing strategies.  There are many different thoughts on marketing, and no universal guides.  What works amazing in one situation works horribly in another. 

It some respects it mirrors the programming code. In some situations any code is appropriate. In some situations specific algorithms would be amazing. In another situation, that same specific algorithm would be terrible. Without knowing a ton of details that don't really fit this format, we can only guess at what marketing strategies might be good.

You need to figure out the goals you've got. If you're looking for building a commercial product you need to get on with figuring out names before marketing begins in earnest. You also need to get all your business details worked out, and understand your business plan.  Marketing of a single game is just a single facet of an overall business plan.