Well, this is a tricky question, since there is no one answer that is correct.
First, use the Insteon Health Tool, run it a few times, and get a decent average to see what s working and what is not.
Second, pull out your existing SignalLinc, and AccessLincs, and try the health tool again.
Next, with the SignalLinc and Accesspoints still disconnected, attempt to optimize your setup as is using the Insteon Health Tool. Â If you have Dual-Band devices, can you switch them around to get optimal coverage? Â etc.
Then introduce the AccessLincs back and test again. Â Does changing the outlet with the Accesspoints improve the performance? Â Once your satisfied, if you have any signallincs, add them back in, checking different outlets to see if it makes a difference.
In the past, the average Access point count is usually been 2-4 depending on the size of the house, if it’s a multiple floor building, etc..  But with the Dual Band devices coming out, it reduces the need for SignalLincs / AccessLincs.  A safe recommendation is that if  possible, when purchasing hardware, purchase dual-band devices…
In my house, I have 2 AccessLincs, and 2 signallincs…
Also, remember, Signallincs are not AccessLincs. Â AccessLincs have a different center frequency, data rate, and better RF hardware. Â I also believe that the Signallincs just repeat the command received by the other signallinc. Â It is simple a repeater, whereas the AccessLincs will also handle as a RF transceiver. Â So remember to have your Wireless devices near a AccessLinc, not a Signallinc.