Yes, high humidity is a problem for a plant in flower or vege for that matter, but extra risk with flowers, since bud rot spreads fast and can ruin an entire grow.
As long as you control RH% as you normal would/should, it'll be fine. Above 65% is to be avoided.
It takes ~2 weeks before seedlings take up any mount of space. Buy a small 2nd light that can cover your seedling tray. You don't need reflective walls or a tent early on.
Unless you use clones of the same plant all the time, the variables involved make perpetual gardens more wasteful and more expensive while reducing overall productivity. Overlapping is a better option more times than not. With minimal investment you can use a 20-30w light to handle seedlings through germination and initial growth before a transplant is needed. That's 15-20 days of overlap with virtually no cost. Don't need refelctive walls for a seedling. A countertop anywhere is fine.
A small tent and 2nd smaller light can handle your entire vege phase, and your grow cycles are only as long as it takes to flower. As far as productivity is concerned, it'll blow a perpetual garden out of the water -- all other factors the same, like wattage used. (apples to apples comparison)