I'm going to be converting my Insight, I'm figuring about 60 pounds of gas, losing the exhaust, power electronics, IMA battery, engine, etc. and adding a controller and reasonably sized motor will probably pull about 200 pounds from the car. 400 pounds of LiFePO4 batteries is a little bit shy of 20kwh. So you'd be about 200 pounds over stock so essentially your 2290lbs GVWR and 1878lbs stock weight plus 200 lbs over stock leaves you with 212 pounds of payload capacity. It works for me and FWIW, I drove my car with a 400+ pound passenger in the past plus my own weight, it drove fine and I don't see much issue as far as a daily driver is concerned if you aren't going to be over the GWVR outside of a rare case.
...but 20kwh of cells, giving you 160wh/mile at 60mph on a good day where it's warm/hot without using air conditioning, without wind, etc. would be 125 miles but you'd be driving the car to nothing, which is what you do not want to do. Of course in the winter, Aerodynamics
are worse, wind is higher, driving through snowy roads and you are using significantly more power to travel at 60mph. I don't think going over 100 miles with an Insight conversion using LiFePO4 is the way to go, especially when it is a situation where you are going to need to do so in the daily driver sense where you want to use the car in any condition. My pack will be 100 60Ah(19.2kwh) cells with a Soliton Jr and the higher voltage Kostov 9 motor. I plan to drive from my house in the Twin Cities area to Rochester, MN just to say I did it and that's a little over 100 miles and there are J1772 stations that I would charge with for me to make the trip back but most of the time I will probably stick to round trips under 80 miles as that should keep me above 30% SOC and allow me some comfort in case I make a wrong turn or encounter a detour or lots of wind along the way.
My project is mostly planned out, waiting on money at this point but I expect to be rolling before the weather gets cold next year. I'm going to try to get the motor soon to get the motor and transmission mated as this is one of the tougher parts to a conversion since there are no decent companies selling an adapter for this car. I have a feeling that if I get the motor and transmission mated and in the car I'm going to be looking to move much faster on the project but I really don't want to work on the car in my uninsulated garage with burning tons of money through my propane heater to get things done so most of this will likely be starting next spring.
If you are willing to give up a little range you can have a car that uses less energy to drive down the road than a Leaf, iMiev, Focus EV, Fit EV, Tesla, etc. and I'm not certain there are any highway capable electric cars out there that could compete with the efficiency of a converted 1st Gen Insight. You also get the advantage of having electric power steering already in the car and a fairly decent space where the IMA battery and power electronics are in the back with a plastic tunnel under the car for the battery cables to go on the way to the front. The efficiency allows for a smaller and therefore lower cost battery. Unfortunately for 150 miles of range you'll have issues with weight and you'd need to pick a car that can handle the extra weight which will then need to be an even bigger battery due to the higher aerodynamic drag such a car would entail, money becomes a bigger issue.
As a gas car, it's a cheap drive for sure. I've gotten three tanks over 800 miles with two of them being over 80mpg. I've driven from Madison and back last month at over 80mpg driving carefully and in perfect conditions without using a/c but not angering other drivers. I drove to Detroit, Michigan and around in town a bit and filled up just under 10 gallons going 750 miles and made the trip home stopping in Madison, WI and got home using just under 10 gallons too. Getting and using MIMA, learning how to drive efficiently with lean-burn and either going the PHEV route with a replacement pack or an add on pack should net you even better MPG within the limits of the battery capacity. I considered going the PHEV route and either using 50 20Ah A123 cells or a pack of 40Ah prismatic cells but decided to ditch the gas and use my other Insight for the out of state trips or trips up to northern MN and do everything else with electric.
My 2 cents
Hope this helps