Creating a rough draft is the most important thing you can do, and a google slide presentation is a great starting point.
Imagine your site is only going to be a long home page with various sections. Many modern sites are just that. But this is more about making your design process more effective.
Each google slide is some section of topic you want to express. If your content for a section is longer than a slide have more slides.
Have a header on each slide that is the would-be page name. About, Mission, Products, and so on... You can get pretty specific if you want, but simple will help you be more effective. Make all the slides / sections you can think of. Don't add any content to them and don't worry about if they are named right or not. Just duplicate and re-name. Go nuts. 2hrs should do it.
Take a second pass at your slides. This time make sure you have at least everything you need, more is better at this point. Also start dragging them up for higher priority and down for lower. 2hrs should do it.
Take a 3rd pass / do it again. Repeat until you have squeezed out all you can tollerate. By this point you should have far more slides than you need, your order will be pretty far off, and the titles will need attention. Basically your Google doc will be a mess - which is perfect!
1st pass don't worry about naming, just drag higher priority section up and lower priority sections down. When you see slides that are essentially duplicate delete the dupes. This should take an hour or less. Don't worry you will be doing more of this you go. This is just just to get you started.
Create a slide that has a black background and big text BELOW SLIDES ARE FUTURE CONSIDERATIONS . This is called a breaker slide.
Drag this slide to where you think it should go, as of now, you can and will move it as you progress. The point is to give yourself a priority line so that you can get something viable live, while also leaving room that more can be done in the future.
Go back and make sure the title and order of all the slides above your breaker slide seem right. Don't spend more than 1hr. Remember this is still a very rough draft.
Start at the top slide and add a text box that is about 25% of the page and use nothing smaller than 11 font.
1st pass - Write in what this slide is intended to be about. Don't write your actual text for the section, instead describe it. Don't spend more than a few minutes per slide.
2nd pass - screenshot images that you think might go with that slide. You should have several per slide. If you are thinking chart grab chart images that you like how they look, don't worry what they are actually about. No more than 10min per slide, even less time if you can.
3rd pass - copy your 'about' text box and write in what could be the actual text summary for that section.
CHOOSE WIX TEMPLATE - OR - KEEP DRAFTING??
By this point you should have a pretty good (high level) idea about your site's priorities, structure, content themes, etc... I recommend you take a tour of the Wix templates. If it feels like you are ready to move on then you should.
Sometimes looking at more polished examples makes my gut tell me that my daft still needs work. If you gut tells you you still need work probably best to listen and do some more drafting. The cool thing about drafting is that by being so simple and rough you can save a lot of time. The better your draft the better AND quicker your site will come together.
You should try to work in block from between 2-4 hours.
How many of those block you need is really up to you. Aim for less than 16hrs.