Look up Hal Higdon for some beginner/intermediate plans, he's pretty good. As said, plenty of time to get the leg muscles in running shape. Just focus on keeping the pace very easy and slowly building up the mileage. With 20 weeks to play with you can afford to build up to a weekly long run over race distance, and as suggested get involved in parkrun for a periodic fitness test/hard tempo run getting used to race effort.
Look up Hal Higdon for some beginner/intermediate plans, he's pretty good. As said, plenty of time to get the leg muscles in running shape. Just focus on keeping the pace very easy and slowly building up the mileage. With 20 weeks to play with you can afford to build up to a weekly long run over race distance, and as suggested get involved in parkrun for a periodic fitness test/hard tempo run getting used to race effort.