You could make the buttons the same red from the logo for color unity instead of gradients (but i dont mind the gradients).
while negative space (empty space) is not your enemy, there is quite a lot. you can fix it by enlarging the text just a bit (1-2.5x)
font is good but try out varying weights of it for the titles, such as the "why choose us..."
maybe include a small content area under the membership boxes for other products available for purchase (small button perhaps)
i think a dark theme instead would have been more logical due to the forums and theme of the client
add a caption under the main client photo to help the visitor understand what they are looking at
there is a lot of padding on the sides but you dont want to have a huge gap between elements on the page, unsure on how to fix this. perhaps enlarge stuff just a tad as well
edit: for the tablet and mobile layouts:
you dont need to put everything on these, i dont want to have to scroll down a super long page just to find the information i am looking for. try to just keep the main driving points of each section and condense them a bit so information is clear and precise on the screen
overall nice job bud