Richard makes a good point.
If it is your intention to run new and secondhand vintage stuff on the track then best to use Hornby as secondhand stuff can derail on Peco points due to tight frogs and rail catchers. If it is your intention to operate with new stuff only and items with finescale wheels then Peco is fine. Code 75 track is harder to work with as a newbie as it is fragile and tricky to cut unless you purchase a rail cutter tool.
I like running the vintage stuff so its Hornby track for me every time and not too fussed by what others say. For a lot of point action in a short space you can't beat set track points.
The only thing is though you mention DCC and therefore there is another issue.
Do you go for insulfrog (self isolating) or electrofrog points (offering more positive running of locos over point frogs as they are live and not plastic).
If electrofrog then it has to be Peco as Hornby don't do these. Peco electrofrog points do make DCC life slightly complex from a wiring and isolating point of view.
Hornby offer a point clip (included with your train set?) that you insert into Hornby self isolating points to make them non isolating which is ideal for DCC as you can then electrify all the track without having a seperate wiring loom and no need to isolate anything.
I am keeping it all as simple and broad as I can. Others can go into the fine detail which no doubt they will!
My BIG tip would be to make the first project a SMALL one and experiment with the track that is available so that you can work out for yourself which is best for you before you start your BIG project!
Happy modelling
Gary