Can anyone give me any pointers that might be helpful ? Is it difficult ?
For receiver, order a Rock River Arms receiver. It's currently the least likely to be out of spec, and one of the lowest priced receivers currently on the market.
As for the kit,
The J&T kit will have a forged front sight tower and will cost you $435.
The M&A and Model 1 sales will have a cast front sight tower and will cost $400.
There are other sources for kits that you can check, but keep in mind that if the company produces a complete rifle, their kits prices will be a little higher to compete with their own rifles.
When you order the receiver, have it sent to your local FFL to do the transfer, Most charge around $20 for the transfer. Remember to talk with the FFL first, before ordering the receiver to confirm that he will do the transfer for you and at a set price.
The kit can be sent directly to you, no FFL needed.
Most importantly, Do not order the kit and receiver from the same supplier, at the same time, or you will pay the added tax required on a complete rifle.
P.S. The kit suppliers I have listed are only a few who are out there. If your looking for sources, the Shotgun news is a great source.
Hope this helps.
If by "kit" you mean "lower reciever parts kit",I know that Rock River and RBPrecision get theirs from DPMS.I'm sure most others do too,so shop around for a good price.