Can I access the main big compartment from the front ??
Absolutely. There is a zipper surrounding the long compartment on the front. The opening is nearly as large as the main compartment. The only issue is that if you really have it stuffed and don't release some of the tension on the load lashes around the pack, it can be hard to zip it back up, but that's not the bag's fault. This is a really great pack for the money. My wife and I each have one.
Yes, there is access to the main compartment from the front. It unzips around the front pocket.