You can use any combination of smaller panels or bricks for replacement. The weight increase can be neglected. If you plan to add a 3rd floor, a winch in the front section with an additional motor, an extra floor in the middle section to mount all the batteries, etc. as you can see in some of the modifications done by others in this thread - that's adding much more weight to the sandcrawler then replacing all the panels with bricks. Another idea for you to consider is to buy 2-4 instances of the 10144 sandcrawler on eBay. That sandcrawler has 16 of the required panels per instance and many other useful brown and dark orange parts (the first 1044 gives you around 800 parts for this MOC).
