I can make some baseline Marketing assumptions here, but again, it's a tough nut to bust crack:
1) Free things will be collected, held, and then never used by the majority of people. This is a value equation thing - there is no compulsion to run something if there was no investment to get it, because there's no nagging thought in the back of the mind saying "you paid for this, so you'd better get your money's worth". However, if you give out an adventure for free, you can bet that people who know about it are going to download it. People love hoarding, especially something they "may use in the future, someday, possibly... or at least poach some ideas from, probably...", and especially if there are comparable products out there that aren't free.
2) In terms of when to drop your adventure: weekdays, for sure - gets them thinking about setting up something for a weekend (games require prep, after all - it needs time to be digested and to get excited about). Evenings are preferable if it's something free, because odds are good that they'll stumble across it during the workday if you release and run hype morning or midday, but they won't be able to download it until they get home, at which point they'll likely have forgotten it exists by then (because it's free, so they don't value it as much - they'll put it in the back of their mind).
3) The baseline audience for serious OSR products is most likely thirty-something professionals. They buy products on cost, practicality, and what they think their group will enjoy. The audience for artsy OSR products is most likely twenty-something hipsters (or people trying to be one). They buy products mostly as showpieces, hipster-cred, and for reading themselves. Both groups have money to spend on products, but the former group are less likely to make impulse buys than the latter (and OSR products are most assuredly impulse buys). The groups aren't necessarily exclusive buys of each genre, but are the most likely buyers. Marketing plans should be skewed accordingly.
4) The OSR field is oversaturated. Too many niche systems. Too many shovelware modules. Too many developers. Paid products have to be really fucking enticing (ie. mucho content, sweet looks, and good reviews) to do well. Free modules just have to be noticed (again, people will collect them but rarely use them - too many options to choose from, and each is a serious time investment).
5) People will crack into material immediately after they've bought it, but often won't if they got it for free (they'll open it, take a quick look, and file it away instead). If they paid money for it, they'll give it a much deeper scan than if they didn't. Deeper scans mean it's more likely they'll run it if they get excited by the ideas they see. For free products to have a comparable effect, your audience needs to see something super-duper exciting in that brief moment they flip across the pages - artwork is the easiest way to accomplish this (draws the eye better). If you release something that's free and too text-heavy, it'll likely never get used at a table, even if the ideas are good.
6) PDFs are less likely to get used than booklets. There's a bigger draw to make use of something tangible than intangible, especially if that something is always sitting around in view/taking up space on a shelf. It's way easier to forget about a PDF nested away under a subfolder on a PC than it is to forget about a physical booklet. Don't assume that more people use PDFs at a table than booklets - not everyone has easy access to tablets/laptops/roll20, but literally everyone can carry around a booklet.
7) Making your product free will move more copies, but will do little for your brand (unless what you've written is paradigm-changing) and even less for your wallet. While you think it may help grow your brand through spreading awareness, it actually harms future sales, because people don't want to pay for things they've gotten free in the past. Charging even a dollar for your product will discourage most of your potential customers (because buying shit online is a hassle, and even a little hassle can turn away a sale), but will greatly increase your product actually getting used at the table. If the product is good, your brand will grow and people will buy more in the future - if it's bad (even mediocre), they'll never buy from you again.
8) Bundled PDFs are less likely to be used overall, even if the customer paid for them. They'll focus on the best thing in the bundle and the rest will fall to the wayside - in the customer's mind, when they buy a bundle they get their money's worth from the best thing and then peace of mind in owning the rest (even though they won't use any of it). If the bundle has many good things (especially critically-acclaimed things), they'll focus exclusively on those and literally never give a second thought to any of the other stuff. On the whole though, when someone buys a bundle, they do it for the comfort of grabbing a dozen things at once for a good deal, not for an actual desire to use any of the products.