Most likely the 10% should be in your original CCR’s. That is the amount assessments can be raised without 2/3 +1 majority of members. ie. just a board meeting vote.
If they have done reserve studies in the past, then there should have a separate reserve account. 2 Accounts, operating and reserve.
Self managed associations are not a bad thing, but may not be up on the, ‘big picture’. My suggestion would be to take a look at what was included in your old reserve study and there will be a dollar amount for each year to be in the bank. Open a new bank account for that amount and separate operating expenses from reserve expenses.
Sounds like no one really cared that much and simply paid for some things outside of a common area expense. ( deck repairs )
If you are businesslike and present the facts that you are underfunded for common area upkeep, you can probably up the monthly assessments to be more in line with actual future replacement costs.
Definitely do not need to spend $ on legal or management. Just show other owners they have ‘overlooked’ some area and we are going to deal with it now.