Id say evaporation could be a problem but only a minor one, you might have to do regular topups, i was tempted to go open top with my own but in the end built a hood for it, and i also made glass covers, i find once the lights are on there is no condensation on the glass covers the heat probably burns it off, but overnight when the lights are off there is quite a build up of condensation the next day on the glass covers, i just leave the glass covers on the tank all the time with a corner cut off for inpipes co2 etc, and remove them if i have to do any rearrangeing of plants and the like.
Last thing, have you thought about a substrate, any final decisions.
Very very last thing are you still going to go with the Dennerele fertilisers or will you become an EI follower and use dry fertilisers, it seems to be the way to go money wise, i was just working out some maths on dry ferts i bought in the last few days, i spent about 20 Euro and probably will spend another 10 Euro (about 20 stg) and that will do all my macro nutrients for more than a year, doseing every second day, so not bad value.