If my charts are showing the mid price then to adjust a buy order for a 0.6 point spread I need to add 0.3 to the desired buy level? Then my stop and limit distances (fixed number of ticks) will likewise have 0.3 added?
Correct; or you could simply adjust your charts to show Ask prices when you're considering longs, and Bid prices when you're considering shorts. You also need to factor this in when placing stops, because if for example you place a short stop and your chart is showing Ask prices, your stop will be in the wrong place.