Novice question

DCS is MTH - since you don't have MTH locos, go with Legacy. As for On30, I think those are DC like HO and would use DCC (not to be confused with DCS)

Welcome to the OGR forums. There are a lot of knowledgeable folks here that can answer your questions. I got back in the hobby in 2011 and it has been a learning experience, like starting all over again. The folks here have helped me a lot. 

If you plan to have Legacy and MTH engines I would get both the full Legacy and DCS systems. You will get more out of each type of engines that way. If Lionel gets their Powerhuouse 180's back in stock, that would be a good source of power. You can power your TIU channels with the PH-180 bricks and then connect Legacy to the common outputs of the TIU and you have it all set up ready to go.

Circuit protection is important for the modern electronic engines. The PH-180s have very good circuit breakers to protect the electronics in your modern engines. The TIU has variable output channels and you can run your postwar trains from those. It isn't all that hard once you get going. 

Hi Novice / Pekelo / Welcome to the OGR Forum.

When I first got started with Lionel Trains in 1983.  I found that local hobby shops and train shows to be very helpful.  Used to go to, Train Clinic, Boxcar Hobbies, Nankin Hardware, Bob Cable Trains and The Birmingham Train Center. Only one of these is still around.

If you can find a local Train Shop, Train Shows and Clubs.  I would suggest this process along with OGR Forum Sponsors and Members.

You may want to take a look at LionChief Plus locos.  My grand children and their friends get a lot of hands on time.  I have four on my layout along with the more advanced MTH / DCS & Lionel.

Take a look at my You Tube Channel for demos, product reviews and running trains at home and at the Detroit Model Railroad Club.

Good Luck - Gary and