The only way to get good long stems and quality (annual) sweet pea blooms is to grow them as cordons - single stems, with all side shoots and tendrils removed almost daily and blooms always picked, whether needed indoors or not.
The most widely grown perennial sweet pea is like fire - a wonderful servant, but ferocious and damaging if it spreads out of control
I'd urge you to consider other wonderful, better behaved perennial pea species, especially Lathyrus rotundifolius which has been a star in my garden, with its bricky pink flowers. Also the dwarf, cerise-flowered L. tuberosus aka the Fyfield Pea.
The black insects are not bugs but pollen beetles. The way I clear them is to hold the bunch of flowers in my hand, extend my arm and swing it round like a windmill, as fast as I dare without wrecking the flowers. It's a similar action to drying lettuce held in a tea towel. The beetles are ejected by centrifugal force.
Nigel Colborn