Adding an additional filter is just asking for vapor lock trouble. It also makes troubleshooting more difficult. The best filter option for a carb is to just replace the tiny threaded carb filter with a hose barb fitting and install an inline filter ahead of it. One large filter is enough.
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Rust and debri can really cause a lot of problems if it sticks one of the valves open. I always run a filter before my electric pump. A $5 filter is a lot cheaper than a $70 pump. I also run one on my mechanical pump as well. Initialy to catch debri from a tank that I had cleaned but didnt get all the debri loose. My lines are run on the outside of my frame for a few reasons. The biggest one bring it keeps them away from exhaust heat. It also makes it easy to see if the filter is full of sediment as well as easy to get to. As far as trouble shooting goes I always keep the replaceable screens for the glass see thru filter in the glovebox. Takes a second to see if there is a bunch if sediment and only a few minutes to change it. I have to think about protecting my pump as well as my carb so its more viable for me to have a filter before and after the pump on my electric set up. Probably not so much on a mechanical but they can get clogged with rust and debri too. I have never run into vapor lock issues so I cant attest to that. I always remove the little filter at the carb inlet and just use a large filter after the pump.
But like I was saying if you are worried about debri from an old tank a filter before the pump is a good safety measure and although it can seem like a hassle having to change it when its stopped up it could prevent other issues down the road.
I really dont see two large volume filters really being an issue. Maybe runing two filters this way is just something I have been fortunate enough to not have a problem with. The first filter just has a replaceable screen so it isnt very restrictive at all and the second before the carb is a mor classic filter style.
