It's a lot of work to do a
It's a lot of work to do a conversion - so I would not recommend it if your car is something like a Honda Accord, because the electric version of that kind of car is the Nissan Leaf or Ford Focus EV. If though you have something real specific you want, go for the conversion, just be prepared for it to take a lot longer than you expect.
As for Lithium versus other battery types - think about the long term cost. Lead acid packs are generally good for 300 charge cycles, and it's easy to find lithium that's good for a couple thousand charge cycles. That's important and amortizes the cost of the pack over more driving range. Also you can take lithium batteries into deeper discharge than you can with lead acid, meaning you get more effective amp hours than you do with lead.