Posted: 30/12/2016 at 12:44
Don't want to rain on your parade Newb, but to give your clematis the best chance of showing themselves off, it's wise to give them adequate room. Rouge Cardinal and Etoile Violette alone will each cover 6 to 8 feet of fence or more, given the right conditions. Forty feet ( eighty in total) isn't a lot of distance for that quantity of plants. You need to be able to reach them for pruning and tying in too, and they'll need a lot of watering and feeding, especially if you have other planting around them. Make sure they all have the right aspect too - Nelly Moser, for instance, looks dreadful in too much sunlight - it needs a shadier spot. Some are happy anywhere but dark ones ( generally) bleach in too much sun and don't look so good.
Clematis are heavy once they've matured, so make sure whatever support you have will do the job. If your fence isn't sound, concrete new posts in and attach trellis - that's probably the best option. Attach wires to the posts if trellis is too expensive, but make sure it's decent stuff, nicely spaced for attaching stems, and well secured.
You could put some of the smaller ones on obelisks but you'll have to tie them in round those as they grow, to get the best from them. Don't make the mistake of just letting them grow vertically.
Hope I haven't put you off - they're among the most rewarding plants if given the right attention and care, but they can look poor if they don't get it