SEO Silo - keywords mixed

Site structure advice like this is normally the type of thing that people pay for to be honest. It's a core component of white-hat SEO. That having been said, I'll type up something real quick to get you started.

NOTE: I began typing my reply when I realize that this question is almost impossible to answer well with the very limited information you provided. I'll do my best but... this is pretty much just going to be a one-sided way of looking at it. All of the data will be skewed by what the keyword lists ACTUALLY are. Further More, I have no idea how tight you want the silo. Extremely tight silo's are often harder to navigate for users than dual-plane silos, as I'm going to talk about briefly below. I'm going to make the assumption that you want to make sales and not just jerk-off Googlebot so my answer will be based on dual-plane silos. Back to the post.....

I'm going to assume that you are using wordpress. Why? Because it runs about 1/6th of the internet.

Your homepage should have content about your primary keyword "E-liquid" and maybe a few longtails about E-liquid that isn't covered in the silo's. You are going to have to make a judgement call here on how you link to your categories and posts from the homepage. I personally run my sites like magazines and have links out to posts within categories directly on the homepage. If you don't do that, consider linking out to categories from the homepage.

In this case, you will want to add custom content to your category pages and have them indexed. The custom content is important for several reasons:

A) To keep them from being purely duplicate content.
B) They will act as landing pages for search traffic and you should be prepared to monetize off them, or at least test monetizing off them.
C) They will complete the silo and without the unique content and having them indexed, you break the silo.

So, figure out what you have to do to add content to your category pages. There's a variety of plugins that will get you there but some themes don't play nice with them. You just need to know from the beginning that they are needed so this is not something you can skip.

From here you will have to actually get into the nuts and bolts of your silo's. Are these keywords the COMPLETE list? We've got to know upfront because it can radically change how you plan your site structure.

For instance, if each individual brand has 2 dozen possible long tails then you may consider making each brand it's own category with "Cheap (brand) E-Liquid" "Buy (brand) E-Liquid" "(brand) E-Liquid Reviews" "(brand) E-Liquid Testimonials" etc being the long tails.

IF each brand doesn't have a few dozen longtails, then it makes more sense to split them up as you have them for the most part. This is really the problem with not knowing exactly what the content strategy is for the site - I can only guess at what you really are working with in terms of keywords. So, you're going to have to figure all of this out before you make any categories, etc.

If you do it this way, then the tagging should be uniform among all of the brand posts. In other words "Cheap (brand 1) E-Liquid" and "Cheap (brand2-xx) E-Liquid" should have the same tags as well, being Cheap E-liquid for instance. By the same token "(brand 1) E-Liquid reviews" and "(brand 2-xx) E-Liquid reviews" should all be tagged uniformly as well with something like "Reviews" or "E-liquid reviews"

TIP: Just like you add custom content to your categories, you should also do the same with the tag pages. This is another reason that the tags between like posts should be uniform among topics - so that you can create effective tag content and create secondary silo's among all reviews for instance - if we were still going on the idea that we had 12-24 longtails per brand name.

Separating by brand in this way also solves the problem with your "Buy" keywords... IE "Buy (brand) E-liquid" will then fall into the silo for the brand it fits with and should be tagged with "Buy E-Liquid."

The bottom line is that you are now breaking up these random words that only vaguely have something to do with each other and giving them specific placements within your domain. Google doesn't really care which words are categories versus which words are tags other than when it comes to the navigation bar - but I solve that pretty easily by putting the tags directly into the navigation as well.

So navigation might look like:

Home - Information (dropdown*) - Brand 1 - Brand 2 - Brand 3 - Brand4 - etc

The information drop down will then link to:
Best Brands
Brand Reviews
Buy E-Liquids
Cheap E-Liquids

That way you are covering all of your silo's in the navigation which is a huge deal because of how Google interacts with/ranks/displays navigation items.

****This was just a real general overview and it's not complete. I have about 1/4 of the total information required to tell you how I would structure the site. I need to know all sorts of other data that just wasn't included in your post and quite frankly, if you do add it later, I won't care. You need to consider how many longtails there are, what the search volumes are, how many 'groups' you really have (fewer brands mean lay out my way, more brands mean lay out in the reverse direction using tags as categories and categories as tags.)

Good luck

EDIT IN: as I read the post, I know some noob is going to roll in and bash the tags. They make the difference between a single-plane silo structure and a dual-plane silo structure. If you are more comfortable jerking off Googlebot and hurting your user experience, then by all means use a traditional single-plane structure and ignore the tags... but I think you would be making a mistake. Some users want to shop by brand, others earlier in the decision process will want to browse reviews first. You're much better offer grouping these things together with the intelligent use of tagging. It also has the side effect of making a tag cloud something that can actually be usable as opposed to a disjointed mess of word soup.

EDIT IN 2: I use tags to simplify my category construction but if you are really against tags, you can also place posts into multiple categories. In other words, instead of having "E-Liquid Reviews" as a tag as described above, you can make it a category as well. The big thing here is the unique content and on a category/tag like reviews it should be aimed to sell or declare and "Winner" to get someone further down the decision making process and onto a commission for you. No need to write a novel, write to sell (or presell). In other words, it's not the place for information - that will go into each individual post. Instead write to summarize the big points on why it is the best and obvious choice for them. 300-600 words typically sells well in my experience - this isn't a long form sales letter! Your reader will fatigue if you do too much there. Besides, you will probably capture impulse buyers here and you can't risk boring them. The buyers that need more detailed information will naturally move on to the full review articles anyways.

Change your name from SEO power to seo idiot.