In vitro transcribed (IVT) RNA therapies are emerging as a revolutionary approach for treating various diseases, though challenges like mRNA stability and delivery efficiency persist. To overcome these problems, we refined IVT RNA vector components, sequence designs, IVT reaction conditions, and lipid nanoparticle (LNP) encapsulation methods to enhance the effectiveness of RNA-based treatments. By fine-tuning the 5' and 3' untranslated regions (UTRs) and optimizing codons in open reading frame sequences within IVT mRNA expression vectors, we achieved improved luciferase expression in both in vitro and in vivo. We also studied the effect of polyA tail length on expression efficiency across different ORFs and cell types, identifying the best tail length for each situation. These adjustments collectively result in the creation of strong and highly effective IVT mRNAs. Our system successfully produced IVT mRNAs, self-amplifying RNAs (saRNAs), and circular RNAs (circRNAs) up to 10 kb in length, with capping efficiencies exceeding 99% and stable polyA tails. We also investigated the effects of nucleotide modifications, such as m1ψ and m5C, finding that expression efficiency varies depending on the specific modification and cell type used. Our LNP encapsulation strategies were tested in various cell lines, including HEK293 and primary T cells, demonstrating successful RNA delivery in vivo. To improve tissue-specific delivery, we created a CD31 antibody-conjugated LNP, which showed a preference for lung tissue targeting. Our platform supports the development of RNA therapeutics, including RNA vaccines development, CRISPR gene editing, and the expression of chimeric antigen receptors (CAR). By leveraging these extensive optimizations, our IVT RNA platform enhances the synthesis and delivery of IVT RNA and provides a powerful toolkit for developing high-efficiency, targeted RNA therapeutics.