Opening Paragraph of James's Portrait

This:

Under certain circumstances there are few hours in life more agreeable than the hour dedicated to the ceremony known as afternoon tea. There are circumstances in which, whether you partake of the tea or not—some people of course never do,—the situation is in itself delightful. Those that I have in mind in beginning to unfold this simple history offered an admirable setting to an innocent pastime. The implements of the little feast had been disposed upon the lawn of an old English country-house, in what I should call the perfect middle of a splendid summer afternoon. Part of the afternoon had waned, but much of it was left, and what was left was of the finest and rarest quality. Real dusk would not arrive for many hours; but the flood of summer light had begun to ebb, the air had grown mellow, the shadows were long upon the smooth, dense turf. They lengthened slowly, however, and the scene expressed that sense of leisure still to come which is perhaps the chief source of one's enjoyment of such a scene at such an hour. From five o'clock to eight is on certain occasions a little eternity; but on such an occasion as this the interval could be only an eternity of pleasure. The persons concerned in it were taking their pleasure quietly, and they were not of the sex which is supposed to furnish the regular votaries of the ceremony I have mentioned. The shadows on the perfect lawn were straight and angular; they were the shadows of an old man sitting in a deep wicker-chair near the low table on which the tea had been served, and of two younger men strolling to and fro, in desultory talk, in front of him. The old man had his cup in his hand; it was an unusually large cup, of a different pattern from the rest of the set and painted in brilliant colours. He disposed of its contents with much circumspection, holding it for a long time close to his chin, with his face turned to the house. His companions had either finished their tea or were indifferent to their privilege; they smoked cigarettes as they continued to stroll. One of them, from time to time, as he passed, looked with a certain attention at the elder man, who, unconscious of observation, rested his eyes upon the rich red front of his dwelling. The house that rose beyond the lawn was a structure to repay such consideration and was the most characteristic object in the peculiarly English picture I have attempted to sketch.

When I first read the novel I thought those three first words were havery non-committal nonsense. Now I tend to think they are an elegant periphrasis for "if one is wealthy" ('Under certain circumstances, those circumstances involving lots of money ...') Also: I wonder how many Jamesian sentences begin with a stressed syllable, as this one does. In the paragraph here we have 'Those that I have in mind...' and 'Part of the afternoon had waned...' But is it true to say that, generally, James prefers to start his sentences with unstressed syllables?