My clematis montana is blooming its head off atop a privacy fence taking up about 8' high and at least as wide. I have given it some space with roses planted about 4' away on each side (8' clearance). There is some intermingling but the clematis is finishing before the roses start and I can cut it back to keep it in bounds somewhat. I grow lots of different kinds of clematis with roses on this fence(more than a dozen varieties of clematis; I've lost track). I have an 8' high x 12' wide section of fence covered with the Sweet Autumn clematis (paniculata) in fall, though I also have two roses and another clematis (jackmanii) planted to bloom at different times in this section. They all intermingle and I cut back only if something is getting suffocated.

I've been doing it, too. I don't plant them in the same hole, but plant the clematis out along the branches of the rose. I, too, like purple clematis with yellow roses, and I'm trying to get two red Niobe clematis to grow with my white Lady Banks but they're a little slow coming along. Just recently I planted a dark montana clematis, I think it is Freda, beside my Veilchenblau rose, and the clematis is blooming beautifully now and the rose is in bud, so I think this will be a nice combination. I've also got a lighter pink montana clematis on an arbor with a yellow lady banks rose and that looks really good right now - both are in full bloom. I am a new fan of montana clematis with their smaller flowers and think they will go really well with roses because they won't outshow them. A lot of the larger-flowered clematis are just really too showy when the rose is in bloom, although they're nice with once-blooming roses because they fill the shrub in with color after the rose has bloomed.

I have Zephirine Drouhin, a shade tolerant, nearly thornless climbing rose with Prince Charles clematis, a light lavender-blue. They don't have a completely overlapping bloom, with ZD beginning first and PC overlapping with the later ZD bloom. Here it is in late June with PC just starting. I have a trellis because ZD and most other climbing roses aren't reliably cane hardy here, so I've never tried this without some supplemental support. You can grow clematis into any stiff-stemmed shrub. One of my favorites is Clematis Little Bas growing into Hydrangea paniculata 'Quickfire'. Here, the clematis starts blooming mid-June with the GF buds, then the bloom overlaps for a couple of weeks, and then the QF continues blooming until frost with the blooms shading slowly to deep pink. Clematis Mikelite and Romatika scrambling around on top of a row of Fothergilla shrubs. The Fothergilla has early spring bloom and stunning autumn foliage color, so this gives it some summer interest. I was inspired to do this a number of years ago by another gardener on this forum, so I am just passing on the enabling.

Type 2 clematis are a bit more challenging to grow than type 3 which are bulletproof in my experience. You are correct that they will want a support structure other than the fence so that they are growing in front of the fence. The trellis should have pieces that are not much larger than pencil width in diameter since they grow by twining the leaf stems. Large slatted trellises an inch or more wide tend to be difficult for the clematis to grab. A few type 2 clematis that I have found relatively easy are Guernsey Cream, a creamy white, and HF Young a mid lavender-blue which varies a lot in how it looks, depending on the light hitting it at different times of the day. Another one, Piilu aka Little Duckling (the translation of the Polish original name) is pink, and is the only one I have ever seen a second bloom on, though it is typically fewer than 5 flowers if any. I never get double blooms here, only single flowers, due to the plant being killed back in winter and losing the flower buds formed the previous year. Flowers on new wood of most doubles tend not to be double (extra petals for additional fullness). Here my growing season is too short for type 2s to bloom twice. They typically are killed back to the snow line here in central NH, so get pruned back like the type 3s. They bloom in late May while the type 3s bloom in summer. I don’t know whether your area will allow for full double blooms or not. The longest blooming clematis I have is a type 3, Rooguchi, which has dark purple-blue bells. It doesn’t climb (basically a tall, lax stemmed perennial) and grows to about 6’ in my garden, so I grow it up the middle of a metal obelisk.I get about 6 weeks of July and August bloom on my mature plant.