That really depends on your experience with working with wood and if you've built anything in the past. My thought is this:

• IF you can understand the plans and what they are telling you AND you have the tools and know how to use them, you could probably build from plans
• If you are unsure about reading plans or don't have the tools needed to make the parts, go with a kit

As far an foam or wood, I would go with wood. While foam is a viable option, it requires glues that are compatible with it. Building from wood allows you to use readily available wood glues, epoxies and CA(otherwise known as super glue). There are a few things you do need to be aware of when it comes to building a plane:
1) Plans generally don't have any instructions so you will need to be able to figure things out as you go while most kits do have instructions included. Sig kits have very detailed instructions included so that you don't have to figure things out, just follow the instructions and you will end up with a flyable plane
2) Since this is your first plane, you will want to build one that is fairly simple. A trainer would be a good option for this as they are generally easier to build
3) Do you have a flying site available and if so, how large is it? A smaller site would make a smaller plane a better choice as they need less room while, on the other hand, a very large open area will be more suited to a larger plane since you will tend to fly it further away and being able to see it can become an issue
4) Do you have any experience flying an R/C aircraft? If you do, you have more options available but, if not, I would recommend sticking to a high wing trainer.

I hope all of this helps