Please advise

[mjyp]

I will be starting up a 125g planted Discus tank, and need to know the following.

Are substrate heating cables worth the expense? If so which one?

If not then a would heated 2128 (Eheim) do the trick? Should I add more heat using external devices?

Was planning on using pwr. compacts 4x65w. Will that be enough light? Tanks dimensions are as follows 72x18x20 125l or 60x18x24 125h. Leaning towards the 72x18x20.

Sorry about all the dumb q's but I want to make sure this gets started right.

Thanks in advance

[GulfCoastAquarian]

Substrate heating cables are questionable for their worth. They can help, but I would focus my expense on more critical areas, such as lighting and CO2. The heated Eheim would work wonderfully. So would a standard high-quality tube heater, but if you do not want the clutter, a filter with an integrated heater is a great way to go.
The four 65w Power Compact lights will provide marginally adequate light for a planted tank. Especially with the taller tank you're contemplating. Also, since you're looking at a six foot wide tank, the 2 foot long 65w PC's will not provide even coverage. I would consider six 65w bulbs or four 96w (3 foot) bulbs to ensure even distribution of light across the entire substrate.