you should have 2 1/2-5 watts per gallon of water, so for a 125 you should have 312-625 watts...that depends on your house temperature. If the tank is say in a basement where the ambient temp. differs a lot, then I'd go with a higher rating, if the air around the tank is close to the temp. you want the tank at, go for the lower rating. But I would suggest #1 with oscars, either have a heater guard or a titanium heater, and #2 also it's better to have a couple smaller heaters throughout the tank than 1 big one. I would think 2 200 watt heaters would be sufficient, unless your house is really cold, then I would get 3 150-200 watt heaters. And if you don't feel like springing for titanium heaters with the oscars, after you get the sump set up, you can put your glass heaters in there and no one will be able to attack them.
and as for sand, if you like the color of regular sand, with a sump, play sand won't be as big of a deal as it is with canisters/hobs so don't be afraid of using the cheap play sand because of that if you like that color (play sand is $3 for 50lbs at lowes). I recommended colorquartz because i like black sand and moon sand is EXPENSIVE....and if you don't want the "dirty" part of the play sand, pool filter sand isn't much more...just make sure you rinse the sand real well, and you'll love it, it is much easier to maintain. I put the sand in a 5 gallon bucket and use the hose to stir it up until the water coming out runs clear, which can take a long time with play sand I've heard, but after that everyone is happy with it (except for the getting into the hob/canister filters)....
and as for sand, if you like the color of regular sand, with a sump, play sand won't be as big of a deal as it is with canisters/hobs so don't be afraid of using the cheap play sand because of that if you like that color (play sand is $3 for 50lbs at lowes). I recommended colorquartz because i like black sand and moon sand is EXPENSIVE....and if you don't want the "dirty" part of the play sand, pool filter sand isn't much more...just make sure you rinse the sand real well, and you'll love it, it is much easier to maintain. I put the sand in a 5 gallon bucket and use the hose to stir it up until the water coming out runs clear, which can take a long time with play sand I've heard, but after that everyone is happy with it (except for the getting into the hob/canister filters)....
