Should be lovely - many people like mixing lard and tallow to get the best of both of them.
Two things - that's not a huge batch, but it is also a bit more than I would make for a test batch of a brand new recipe. If I was making a small tweak to an existing one, maybe, but something totally new............? I would stick to 500g. Also, are you using the "Water as % of oils" setting, or one of the other 2 water options? The two other options allow for much more control (= consistency in your results) than the % of oils option.