DCS TIU

Will using all three of them cause any problems

No, not at all, although I suggest that you set them up in Super TIU mode.

and are there things that I need to look out for? 

I'm sure that there are, however, you really need to be more specific.

Getting the TIU set up can get a little tricky.  Each one will have to have  it's own address. TIU 1. 2 &3.  , This is where most make a mistake.... They add  the tiu before editing the address. ( unfortunately dcs will let you do this) Now  you may think you've added the correct  tiu but you haven't. There's a red LED on top of each tiu that lights up and flashes each time the tiu powers up. Each or blink is the actual tiu number.   So you may have to delete, edit, and eventually add to get the tiu set up  correctly..

Deleting a TIU can also delete your engines from the remote.

Bottom line , The red led blinks are very important.... Once you get all the tiu set up you can verify with the "read ." bottom left on the remote. You should get something like TIU 1, tiu 2 ,and  TIU #3 found.... Now's the time to slip them in super mode under the TIU menu (super tiu). SPR.

GRANDPAD,

    The one general thing I would caution you about is having all your TIU's and Hand Held Remote Controls upgraded to the the latest revisions, I had a run away off the 2nd level a few years back, that cost me a few bucks in repairs, because mine were at different rev levels.  Barry was the one that caught my mistake, had it fixed and everything works well now.

PCRR/Dave

Grandpad, The above advice is not just good advice, it is essential advice.  As Gregg says, before starting any TIU installation or loading of locos, start each one up individually.  They will probably have ID addresses of #1, although given their ages they may have been changed.  Set them as #1, #2, & #3, using the remote's setup.  As PCRR/Dave says, upgrade all your remotes and all your TIUs to the latest version of the software, version 5.0.  Then, as Barry & Gregg say, on each remote set each TIU to super mode.

If there is any possibility of adding a 4th remote some day, I would strongly recommend numbering the 3 you have as 2,3,&4, leaving #1 slot vacant.  It will simplify life in the future.

I also recommend that, after your get all the locos loaded, and the softkeys arranged the way you want them, that you back up the remote to a computer using the Loader program.

Thanks for all the help. I hope that I will see you at York. I will be at the Dunham Studios Booth Most of the time.  John