Ok my first question is always why do you think LSN?
not to doubt you at all, you of course know your LO best
but many people make the assumption that LO is LSN because they aren't having much sleep, but in fact chronic overtiredness can look very similar. However if LO is napping (reasonably) well, waking happy and sleeping well at night then LSN may well be the case. If you do want any help on that front though we are more than happy to help
In terms of how the day could look with 3.5h A times (assuming 7am WU)
WU 7
Nap 10.30-12
Nap 3.30-4.30/5
BT 8
Milk on WU and at BT with solids an hour after milk in the day. If your LO isn't having much solids yet you may need to do top-ups 30 mins or so pre-nap to avoid wakings from hunger x