I require all new tenants to use it, but I have a few that use other methods due to them being tenants when I acquired the properties.Background and credit checks are easy to send to an applicant - they pay 55.00 and I get the reports quickly. 

Consider that on many SFH with the BRRRR method you rent and hope to get a few hundred a month free and clear.

This took away the LL capability to not renew lease or, my preferred method, provide large rent increase above market to get rid of less than ideal tenants.  

yeah i believe the instulation is R22 Rock solid, R5 sxp foam on the concrete, and the dry wall is something like 5/8th thick.

A lot of mistakes can be made if you do not talk to the right people and use preventive maintenance to avoid problems.Multifamily rentals are a great way to use the more doors more cash flow method.

Any online method i can ask tenant to use that can deposit the amount to my bank account which is free for tenants and safe method for me to use. i had issue with one of the check send by tenants (not a tenant fault)and i was about to fall into scam as i tried to deposit the check online but now want to stay away from Checks. venmo/zelle doesn't allow bigger amount transfer.

I suppose one method would be to use seller reported figures but that wouldn't be prudent for many obvious reasons. 

This method saves time and keeps a record of everything you or your employees ever told them. 

The next downturn could be a repeat, if the subsidies dry up and the dumb money stops coming in, propping up prices. 

I agree with @Michael Plaks that the pricing should be discussed prior to the start of the engagement.My firm does not like the hourly invoice method because I find it can potentially cause anxiety to clients who may not know the final price.if you were a nice client and paid an hourly fee, maybe there was a lot of time towards 'setting' you up as a client(inputting your properties, prior year carryforwards, depreciation schedule, etc) which won't be a cost for you going forward.Best of luck.