You may want to consult your microbiologist before switching to entero totally. On my understanding the difference between the analysis of the 2 is that for salmonella you pre enrich you swab samples, meaning if you have one salmonella cell this may turn positive with your analysis (depending on what method you will choose) as you pre enrich the sample (meaning you give its ambient condition to grow at this period of analysis). Where as for entero (EB), you analyze as is (after addition of buffer diluent, meaning what you have in the swab will not grow provided you handle your sample well) and normally what you use depending on the analysis is either <1 cfu/swab or <10 cfu/swab. So in this case, you may have <10cfu/swab but your salmonella swab may turned to be positive. This is only for the point of view of analysis.
Another thing, you may also want to review how you do swabbing. Are you using multiple swab? Wherein you swab first for Entero followed by Salmonella? or you swab at different point or same points? Or you one swab to analyze for both? Depending on the method, you may not see some alignment for the result. In example, you swab one point which on your point of view is heavily contaminated. So "most" of the cell may be removed by the first swabbed, then you swab again at the same spot. It may turn out your first swab will have high counts then your second swab may turn to be negative.
3rd, you may want to review risk assessment. As oppose to other view here, I consider EMP as relevant to "prevent" microbial contamination going to your product as it is perform not to check cleaning only (as it would be cleaning verification) but it also consider other GMP (such as zoning, prevention of microbioligical contamination, routine maintenance, etc.) .The output will be dependent on how you assess your line and what sampling points you will take. The frequency may then be reviewed in according to how high is the risk for your product to support microbial growth.
In terms of construction, this again will depend on the scope of work. However what is fixed is that permit must be taken before the activity (to which line manager needs to release the area before we allow contractors to go in), installation of enclosure depending on activity, if bringing tools from outside we do sanitize and take samples, and lastly, area will be released in terms of foreign materials and we also take samples after cleaning.