1. Who is Embraer’s major competitor?

As has been mentioned Bombardier with their CRJ line. Later perhaps Fairchild Dornier/D’Long Fairchild, whatever it will be called. Second hand planes should also be considered, mainly the F70/100 and the BAe-146/ARJ.

2. Is Embraer going to keep maufacturing regional airliners or is the company going to start producing aircraft that will encrouch on Boeing’s and Airbus markets for large aircraft?

Would that really be a wise thing to do? Do they have enough (financial) muscle to annoy Boeing and Airbus. On the other hand, the basic 737 design is showing its age and won’t last forever. This may be the best moment for quite a while to come to start such a project. Would they have enough money to do that as I suspect the 170/190 series costed them quite a few quid.

3. The 195 is the largest plane in their line up, (I think). Is Embraer planning on designing a larger plane?

No, nothing has been announced anyway. Please refer to my answer on question 2.
For the foreseeable future they will probably be quite busy with the 170/190 series. Even when the first deliveries are being made. New versions WILL come up, business jet/shuttle, various military tasks, longer range, more quiet etc.

4. What is most comprable to the 170/190/195 line?

The 170 can be compared to the B712 and second hand F70s and the smaller BAe-146s and ARJs.
The 190 with the F100, the larger BAe-146s and ARJs, A318, B736 and if it will ever be build the B713. The A318 and B736 are very heavy though! This will not make them as efficient to use as the 190/F100 and probably ARJ (don’t know for sure). For an airline requiring long range they will be very good, for airlines with extensive families of B737NGs/A320series too.