Typical cost range for adding or replacing a 2-pole 220 breaker generally falls between $85 and $680, with most residential installations landing around the $125–$250 mark for a standard 20–30A breaker. For higher amperages, AFCI/GFCI protection, or difficult access panels.
September and October are the optimal months to install solar. Wait times are 3-4 weeks (vs 6-10 in summer), weather is ideal for roofing, and your system is ready for the full high-production season starting in March.
Though mixing different solar panels is not recommended, it's not forbidden and things would be ok as long as each panel's electrical parameters (voltage, wattage, amps) are carefully considered. When you intend to wire two panels produced by different vendors, the vendors are.