Profoto flash gear is terrifically overpriced per Watt-second.
Not nearly as bad as the shelves full of Broncolor I have. However, most are going on 30 years old and every one still functions 100%, so long term they're not so bad.
To the OP,
I'm not sure what your experience level is, what formal training you have in the visual arts, technical skill level, etc. From my perspective, as a working commercial shooter for 30 years, is that your lack of vision is actually not the biggest problem, the clients lack of coherent branding and a creative direction is. The fact that they're leaving every aspect of creating images up to you is the real issue.
Back in the old days, when clients hired agencies, creative directors or art directors went to studios and oversaw the image capture process, before you got into the studio, there was a pretty firm shoot list, as well as some ad dummies (called blue lines) that would have important placement areas traced onto Mylar and put on the ground glass of the view camera. The important thing to note is that all of the major design and composition was already determined long before you even got into the studio. The majority of CD's and AD's had BA or BFA degrees in design, understood composition, color theory, the psychology of advertising/imaging and branding.
While agencies still exist, few companies use them anymore, seeing them as an unnecessary expense, and it shows in the huge number of horrible logos, ads, and other ephemeral material poorly designed and implemented.
This is what you're real issue is, there is no clearly defined "look", as Derrel said, there's no direction. Meet with the client, with a sketch pad and pencil, and block out some concepts. Refine the composition until it "works". Then, and only then, set up equipment. As far as lighting equipment, you're at a tremendous disadvantage having only been shooting for a few years (as an aside, when I ran a studio an assistant typically worked for me for two to three years before they were let loose as a shooter. And that's somebody with a bachelors degree in photography).
You said you need fill light, and I'd agree. Dark walls aren't the problem, the lack of a couple of sheets of foam core is. In a perfect world, I'd fly a big soft box over the set and use plenty of fill cards. Since you can't, improvise, a couple of sheets of foam core behind,lit by natural lighting, will do wonders. I'm not sure how conversant and knowledgable you are with regards to lighting, but in the commercial world, light is everything. If you decide to use strobes, you'll need to block off the windows 100%, and light everything or gel your lights to match ambient, (and I'm guessing you don't have a color temperature meter) otherwise the slight difference between ambient and strobe will give your shadows a different white balance than your highlights.
Unfortunately, you've made some decisions regarding equipment needs that you've now come to realize aren't quite right. 99% of the time any modern body will do just fine. Personally I still use my kodak SLR/n for almost all of my food and product work, and a drawer full of Nikon manual focus lenses. I have over a dozen bodies to choose from, ranging from a Nikon D1x to a D3, as well as digital backs for the Hassy and Sinar view cameras. While many may disagree, is not the camera, it's the photographer that creates truly effective images. In commercial work you really don't need 2.8 zooms, iso 6400, huge image sizes,etc....though many will say you do. (Aka, the Internet forum effect)
Base ISO, fixed focal length lenses (typically the slower lenses are far better optically) and effective lighting techniques are what is required to make good images. I'm assuming you have a copy of Light, Science and Magic, probably the best single source for learning effective lighting techniques. I'd also suggest some formal training, color theory, compositional design and general art classes can help tremendously in every visual art.