What is a good % grade for Ho ?
Probably in the range of 1.5 to 2 % would be acceptible ; any more starts leading to slippage and reduced towing capacity.
3% is considered maximum.
Most grade situations are driven by layout size. You grade will be the a function of the length of track needed to cross over another section of track. You can save a little space by using a shallow bridge vice plywood and roadbed at the crossover point. A figure 8 layout on a 4x8 sheet of plywood will probably have more than a 4% grade yet many folks make this work by using few cars and keeping train length at a minimum. Be sure to make the transition from flat to grade (up or down) a gradual one or you'lll get a shoestring effect and derailments. Most home layouts have between 2% and 6% with the really largest able to have less than 2%.
Hope this helps,
Robin
Kind of a rule of thumb:
Main Line operations; long trains - Keep to 2% or less
Branch Line/Short Line; fairly short trains - Up to 3%
Logging, Mining, special operations - Up to 4%; logging maybe 5% with geared locos.
The only grades I have are the transitions from mainline to the freight yards. I have gradual tapered beds made of balsa for the drill leads, so the grade is only about 2%. Moving several cars around with the short switcher presents no problem. I would prefer a lesser grade, but I'm limited with the 4 X 8 layout.
As mentioned, avoid abrubt elevation changes.