Scale are a pain to get rid of, by the time ypu see them theres loads more to come, the alcohol such as meths or isopropanol works dabbed on them, i have added a 5% ml of isopropanol to a lite of water and water or neem oil and water spray, both will kill them, as will 5ml per litre of limonene ( citrus oil ) spray
If you use a systemic insecticide , most arent tested/licenced for use on citrus that are eaten as they stay in the fruit, so best to avoid systemics if you can if you plan to eat the fruit
The way used in the citrus groves to kill and prevent most pests is to put a teaspoon in a litre of water of horticultural oil ( odourless mineral oil / kerrosene ), they tend to use nothing stronger most times, it also works on spider mites , i use neem oil it works the same
With the number of flowers, its just got more this year probably as its older or due to the amount of cold hours this winter ( if it got more time colder below 12C) , its best to leave all flowers and fruit to sort themselves out, a tree will thin them iteslf if needed ,
A recent study in the states has found removing flowers or fruit even from a young tree has no effect on speed of growth of roots or the top so best to leave them as most will drop,
You tend to loose something like 95+% of the flowers before they get to fully grown fruit even on a mature 40+ year old tree so theres no need to remove them and they look good
A way of getting more fruit to stay on the tree without dropping is to spray the tree just before/at the time it flowers with a teaspoon of saltpeter ( pottasium nitrate ) per litre of water on the leaves