"investment in Thailand".. this is an oxymoron. You don't 'invest' in Thailand. You spend money here, with no expectations of ever seeing a real return. As the old saying goes; invest in home.. spend in Thailand.
In theory, yes. In reality, it probably isn't a bad idea to think about ways to save up for an elite visa, just in case the DTV program gets cancelled.
The good thing about the UK is the summer and the bad thing about Thailand is the rainy season. Luckily these both happen at the same time, so it might be worth thinking about spending half the year in Thailand (in the UK winter) and half the year in the UK, in the UK summer. In other words, don't spend more than 180 days in Thailand per year, then you don't have to worry about this.